West, Ian M. 2013. The Isle of Portland: Geology of the Quarries. Part of the Geology of the Wessex Coast (Jurassic Coast - Dorset and East Devon UNESCO World Heritage Site). Geological field description. http://www.southampton.ac.uk/~imw/Portland-Quarries.htm. Version: 19th December 2012.

Isle of Portland, Dorset - the Geology of the Quarries

Ian West,

Romsey, Hampshire
and Visiting Scientist at:
Faculty of Natural and Environmental Sciences,
Southampton University,

Webpage hosted by courtesy of iSolutions, Southampton University
Aerial photographs by courtesy of The Channel Coastal Observatory , National Oceanography Centre, Southampton.
Website archived at the British Library

|Home and Contents |Geological Introduction to the Isle of Portland |Portland Bill |Portland - dinosaur footprints |Portland - Mutton Cove to Wallsend |Portland Harbour |Withies Wall, Portland |Portland Group Fossils |Portland Bibliography
Selected External links: Jurassic Coast - World Heritage Site | Mark Godden's Portland Quarrying Website.

Click here for the full LIST OF WEBPAGES

(You can download this educational site to SurfOffline, or similar software to keep an offline copy, but note that updating of the live version takes place periodically.)

Underground mining of Portland stone at Bowers Quarry, Isle of Portland, 7th June 2008

A wide-bodied giant ammonite of Titanites type in the Portland Roach, Isle of Portland Dorset

Go back to top

Isle of Portland -List of Field Guides and Bibliographies

Isle of Portland - Geological Introduction
Isle of Portland - Geology of the Inland Quarries (this webpage)
Portland, West Side, Mutton Cove to Wallsend
Portland, West Side, Mutton Cove to Wallsend
Portland Bill Geology
Portland Harbour
Withies Wall, Quarry Section, northern Isle of Portland
Chesil Beach - Introduction
Chesil Beach Pebbles
Chesil Beach Lodestone, Magnetite Occurrence
Chesil Beach - Storms and Sea Defences
Chesil Beach - Bibliography and References
Dinosaur Footprints, Purbeck Group, Isle of Portland
Bibliography of Portland and Portland Stone Geology

Go back to top

PORTLAND - INTRODUCTION
Safety on Field Trips to Portland Quarries

This webpage is a description of certain geological features and many include photographs and descriptions of coastal scenary, cliffs and quarries. It may give geological guidance but it is not an itinerary or practical field guide or programme, nor does it represent advice to go to any particular place. In fact, it may be impossible to go to some places described. The objective is to provide geological information. Any field trip programme is the responsibility of the individual, or the leader or the organiser or the organisation.

Some specific hazards with regard to geological study on Portland are mentioned here, but the subject is not covered comprehensively. Like almost everywhere else on the Dorset coast care must be taken with regard to hazard of falling rocks. There are also hazardous cliff edges; artificial cliff edges in quarries are sometimes less obvious than coastal cliff edges and should be watched out for.

On the Isle of Portland safety helmets should be worn beneath cliffs and in quarries, and places where it is clear that rock has recently fallen should be strictly avoided. Quarry regulations must be followed. High-vis jackets or tabards are normal in quarries. In particular care taken to keep clear of heavy plant and machinery. Large vehicles, JCBs etc, may appear quite suddenly on quarry tracks and quarry working floors, and it is not necessarily clear in which direction the vehicle is heading. Obviously keep away from motorised rock saws or other machinery. Get of the way quickly and move to a place of safety away from the trackway or working location.

It is important not to hammer the chert in the Portland and Purbeck strata because of very dangerous. Take care not to fall down fissures in the Portland Stone and do not enter fissures or caves without the normal caving safety precautions.

Access to Albion Stone quarries, mines or quarry works or factory is only possible with permission from the company. Abide by their regulations and warning notices and, of course, always follow the instructions of the manager or guide.

Go back to top

PORTLAND, GENERAL GEOLOGY
The Geological Succession

For introductory information go to:

Geological Introduction to the Isle of Portland

Go back to top

BUILDING STONE

Portland Stone as a Building Stone

(For Portland Building Stone at Portland Bill see also Portland Bill Field Guide)

Like most famous building stone, that on Portland was known to the Romans. The stone was worked intemittently throughout the Middle Ages. In the early fourteenth century some stone was sent to Exeter for use at the cathedral and some to London for the Palace of Westminster (Leary, 1983). But it was not until the seventeenth century, with the introduction of frame saws and water power, that cutting so hard a stone became economic on a large scale.

King James I appointed Inigo Jones as chief architect and surveyor-general. Under this appointment, Jones was required to survey the Crown lands on the Isle of Portland and it was he who first brought the stone, in quantity, to London. In 1619 he used Portland Stone to build the Great Banqueting Hall of Whitehall Palace and later for restoration work at St. Paul's Cathedral (Leary, 1983).

The introduction of Portland Stone to London is celebrated in a contemporary poem (North, 1930).

Portland Stone in Pauls Churchyard. Their Birth, their Mirth, their Thankfulness and Advertisement, - by Henry Farley, 1622

"ere since the Architect of Heavens's fair frame
Did make the World, and man to use the same;
In Earth's wide wombe, as in our nat'rall bed,
We have beene hid, conceal'd, and covered,
Where many thousand ships have sailed by
But knew us not, and therefore let us lye,
Till at last, and very lately too. . .
We were discover'd, and to London sent,
and by good Artists tryde incontinent;
Who (finding us in all things firme and sound,
Fairer and greater than elsewhere are found)
did well approve our worth above them All
Unto the King for Service at Whitehall"

("....written by Hen. Farley, who hath done as freely for Freestone .. as most men, and knows as much of their mindes as any man ... to be sold at the great south door of Paules, London.")

After the Great Fire of London, in 1666, Portland Stone was extensively used in rebuilding.

Sir Christopher Wren used it in St. Paul's Cathedral and in many of his churches, and for a time the Portland quarries were, by the King's command, worked exclusively to supply stone for the Cathedral. It was built from Portland oolite of the Grove Quarries on the east cliff, from the area where the old prison now exists to the later Nicodemus Knob.

Other London buildings in which Portland Stone was used include the British Museum (1753) and Somerset House (1776). Smeaton used it in his Eddystone Lighthouse (1756) and there are many examples of its use in important provincial buildings. It is used in the facade of Waterloo Station, the ICI building at Millbank, Vintry House (of the Vintners' Company) near Southwark Bridge. It has been used for public buildings in Cathays Park, Cardiff including the National Museum of Wales. It has been used for the Civic Centre, Southampton. A modern carving is the great group of statuary by Benjamin Clemens, high up on the front of Africa House, Kingsway London (North, 1930). Representative inhabitants and animals of Africa are grouped around Britannia who sits upon a throne.

Other use of the Portland Stone in London includes Somerset House (1776-1792), County Hall (1933). It was used by Wren for dressings in the Fountains Court at Hampton Court Palace. In Cambridge it has been used for the Fellow's Building at King's College (1723-29) and in the Senate House (1722-1730), both built by Gibbs. In the following century it was used for the Old University Library and for the Fitzwilliam Museum. Most of the principal Georgian buildings in Dublin are partly or completely faced in Portland.

The London Cenotaph, 120 tons in weight, was built of Portland Stone from stone quarried in Tithe no. 1269 in the village of Wakeham almost on the site of the parsonage house, destroyed by Oliver Cromwell. The Cenotaph was erected in 1920 by Messrs. Holland, Hannen and Cubitts Ltd. The quarry was filled in 1924 and is now allotments (Pushman, 1987). It is interesting to note that the Cenotaph was designed by Lutyens in only ten minutes!.

Go back to top

BUILDING STONE
- Report of 1839 re Stone for Houses of Parliament

"Report on [Use of Portland Stone] with Reference to the Selection of Stone for Building the new Houses of Parliament. Presented March 1839. (From Damon (1884, pp. 94-95).

St. Paul's Cathedral, London. Finished about 1700. Built of Portland Oolite from the Grove Quarries on the east cliff. The building generally in good condition, especially the north and east fronts. The carvings of flowers, fruits, and other ornaments, are throughout nearly as perfect as when first executed, although much blackened. On the south and west fronts larger portions of the stone may be observed of their natural colour than on the north and east fronts, occasioned by a very slight decomposition of the surface. The stone in the drum of the dome and in the cupola above appears not to have been so well selected as the rest; nevertheless, acarcely any appreciable decay has taken place in those parts.

Portland New Church, built 1776. Portland Oolite. Fine Roach. In a perfect state of preservation, exhibiting the original tool-marks.

Portland Old Church [Church Ope Cove]. In ruins, near Bow and Arrow Castle (15th Century); of Portland Oolite, resembling Top Bed [Whit Bed]; in very good condition; original tool-marks still appear in the north front.

Portland Bow and Arrow Castle [Rufus Castle, Church Ope Cove]. Many centuries old; of Portland Oolite. The ashlar resembles the Top Bed [Whit Bed], and is in perfect condition; the quoins and corbels of the machicolated parapet appear to be of the Cap Bed of Portland Oolite [is this the Skull Cap or Top Cap, i.e. Basal Purbecks?], and are in good condition.

Wyke Church (15th Century) [Wyke Regis]. Of Oolite similar to Portland; the whole in good condition, except the mullions, tracery, and dressings of doors and windows, which are constructed of a soft material, and all all decomposed. On the south side the ashlar is in part covered with rough cast. The entire building is thickly covered with lichen.

Sandsfoot Castle, near Weymouth, constructed of Portland Oolite in the time of Henry VIII., is an example of that material in excellent condition; a few decomposed stones used in the interior, and which are exceptions to this fact, being from another Oolite in the immediate vicinity of the castle [presumably the Osmington Oolite of the Corallian]."

Damon (1884) continues:

"The Report from which the above extracts are taken states that buildings situated in the country possess a great advantage over those in populous and smoky towns, owing to lichens with which they are covered in such situations, and which seem to exercise a protective influence against the ordinary causes of the decomposition of the stone upon which they grow. As an instance of the difference of degree of durability in the same material, according as it is exposed to the effects of the atmosphere in town or country, the report calls attention to the several frustra of columns, and other blocks of stone, which were quarried at the time of the erection of St. Paul's Cathedral, and are now lying in the Island of Portland, near the quarries from whence they were obtained [presumbly somewhere on the East Weare?]. These blocks are covered. with lichens, and though they have been exposed to all the vicissitudes of a marine atmosphere for more than 180 years, they still exhibit, beneath their lichen, their original form, even to the marks of the chisel employed upon them; while the stone which was taken from the same quarries and placed in the cathedral itself, is, in those parts which are exposed to the south and south-west winds, found in many instances to be fast mouldering away."

Go back to top

QUARRIES



Go back to top

QUARRIES - A

Go back to top

QUARRIES - OLD LOCATION MAP:


Location of quarries on an old, 1930, map of northern Isle of Portland, Dorset

Go back to top

QUARRIES AND MINES - A

Albion Stone - Jordans Mine

(Under the Red Triangle Cricket Pitch, north of Reforne Street)

The entrance area of Jordans Mine, next to Inmosthay Quarries, Isle of Portland, Dorset, 29th March 2012

Entrance to Jordans Mine in the Whit Bed, Portland Stone, Isle of Portland, Dorset, 2011

Drives and cross-cuts of Jordans Mine, Albion Stone, Isle of  Portland, Dorset, 2011

Inside the wide tunnels of Jordans Mine, Albion Stone, Isle of Portland, Dorset, 2011

Rock cutting machine, underground in Jordans Mine, Portland, Dorset, 2011

Slots are cut in Portland Stone, the Whit Bed, by a computer-controlled machine, Jordans Mine, Isle of Portland, Dorset, 29th March 2012

Portland Whit Bed in Jordans Mine, Portland, Dorset, cut and reading for moving by wedging, 2011

There is remarkable underground quarrying in the Inmosthay area of Portland. The Portland Freestone Whit Bed is being quarried in wide but shallow mines by Albion Stone, using motorised rock saws. The roof is secure, rock-bolted, basal Purbeck limestone. This mine has been successfully planned by Manager, Mark Godden.

Mark Godden explains the use of metal pillows for wedging out the blocks of Portland Stone, Jordans Mine, Isle of Portland, Dorset, 29th March 2012

Plant debris in a thin basal Purbeck palaeosol, Jordans Mine, Isle of Portland, Dorset, 2011

The roof of the mine is marked by the lowest carbonaceous parting in the basal Purbeck Group. This is lower than the Lower Dirt Bed. It is at the base of the Skull Cap and above the Transition Bed. It contains some type of plant debris. This was found by Mark Godden and pointed out by him during a visit to the mine. I photographed some of it and an image is shown above. It was thought at first that it might be impression of roots of plants. However some flattened pieces resemble the fronds of cycadophytes, which were known to be present in the basal Purbeck Group (mostly in the Lower Dirt Bed, a short distance above).

Shelly patch reefs, apparently downcutting at the base, Jordan Mine, Isle of Portland, Dorset, 2011

The base of an oyster patch reef at Jordans Mine, Albion Stone Company, Portland, Dorset, 29th March 2012

Under investigation by Mark Godden are shelly patch-reefs seen in Jordans Mine. These have been described in surface quarries Fursich et al. (1994). The examples in the mine, shown above, seem to show downcutting at the base, according to Mark Godden. This phenomenon is difficult to explain.

Go back to top

QUARRIES - A:

ALBION STONE QUARRIES (INMOSTHAY ETC) AND FACTORY
(See Albion Stone Quarries and Mines by name - Bowers Quarry and Mine, Fancy Beach, Inmosthay Quarry, Jordans Mine etc.)

Particularly see: Mark Godden's Portland Quarrying Website. This is a particularly valuable website, provided by Mark Godden, the Manager of Albion Stone quarries on Portland. He is a Chartered Geologist of the Geological Society of London.

A cliff face of Portland Freestone in Inmosthay Quarry, Albion Stone, Isle of Portland, Dorset, 29th March 2012

The Base Bed in a face at Inmosthay Quarry, Albion Stone, Isle of Portland, Dorset, 29th March 2012

Moulds after aragonitic bivalves, Base Bed, Portland Freestone, Inmosthay Quarry, Albion Stone, Ise of Portland, Dorset, 29th March 2012

Motorised saw used in the Inmosthay Portland Stone quarry of Albion Stone, Isle of Portland, Dorset, 2011

Sawing of a large block of Portland Stone in Inmosthay Quarry, Albion Stone, Isle of Portland, Dorset, 29th March 2012

A large block of Portland Stone is lifted away, Inmosthay Quarry, Albion Stone, Isle of Portland, Dorset, 2011

Quarried blocks of Portland Stone, measured and labelled, Inmosthay Quarries, Albion Stone, Isle of Portland, Dorset, 2011

Blocks of Portland Roach, numbered and ready for cutting, Inmosthay Quarries, Isle of Portland, Dorset, 2011

A large rotary diamond saw, cutting Portland Stone, at the Albion Stone factory, Easton, Isle of Portland, Dorset

A groove-cutting machine processing Portland Stone at the Albion Stone Factory, Isle of Portland, Dorset, 29th March 2012

Work by masons on ornamental blocks of Portland Stone at the Albion Stone Factory, Isle of Portland, Dorset

Stocks of sawn Portland Stone outside the Albion Factory, Easton Street, Isle of Portland, Dorset, 2011

Albion Stone PLC is a very large producer of sawn and carved Portland Stone. The works are very impressive and so too is the steady rate of production of ornamental and building stone from the Portland Stone. The company has extensive large quarries and mines in the northern part of the Isle of Portland. It is the place to purchase various types of Portland Stone and is well-known internationally.

The geology of the quarries and mines is, to some extent, discussed in separate sections of this webpage, under the name of the quarry or mine, shown alphabetically. Albion Stone provides Portland Stone for buildings in Britain and overseas.

Go back to top

ALBION STONE QUARRIES (INMOSTHAY ETC)

Oyster Patch Reefs of the Top Whit Bed ("Shelly Whit Bed")

A simple map showing the general locations of oyster patch reefs, Portland Stone, Isle of Portland, Dorset, after Fursich

Part of an oyster patch reef in the Portland Freestone, Inmosthay Quarry, Isle of Portland, Dorset, 29th March 2012

Details of borings into an aragonitic bivalve shell, since dissolved, Patch Reef, Portland Stone, Inmosthay Quarry, Portland, Dorset, 29th March 2012

Internal mould of <I>Lithophaga subcylindrica</I>, the common lithophagid boring bivalve of the oyster patch reefs of the Portland Freestone, Inmosthay Quarry, Isle of  Portland, Dorset, 29th March 2012

Oyster patch reefs occur near the top of the Portland Freestone. These have been described by Fursich, Palmer and Goodyear. (1997) (in the journal Palaeontology, vol. 37.). Their abstract provides a brief explanation of the reefs and thus is given below:

"Patch reefs, up to 4 metres high and 8 metres across, grew amongst oolith shoals at the top of the Portland Limestone Formation (Portlandian, Upper Jurassic) on the Isle of Portland, southern England. Principal reef framebuilders, which provided between 55 and 70 per cent of the reef volume, were cementing bivalves, solenoporacean algae, and bryozoans. The remaining pore-space in the reef was filled by sediment, most of which is in the form of a precipitated peloidal cement. The cement lithified the reef while it was still exposed on the sea floor, and was probably precipitated under bacterial control. A diverse accessory fauna of small cementing encrusters and nestlers includes groups such as terebratulid brachiopods and lithistid sponges -that have not previously been found in the Portland Limestone. Serpula (Cycloserpula) striatissima sp. novo and Carterochaena pulcherrima gen. et sp. novo are described. Both the primary organic framework of the reef and the submarine cements were bored by a variety of endoliths, which locally removed as much as 40 per cent of the reef volume. Vacated borings acted as sites for precipitation of further peloidal cement. Borings are well preserved as natural three-dimensional casts in cases where they originally perforated an aragonite substrate which has since dissolved. New taxa of borings consist of Cunctichnus probans ichnogen. et ichnosp. nov., Spirichnus spiralis ichnogen. et ichnosp. nov., Talpina bromleyi ichnosp. nov., and Entobia cervicornis ichnosp. novo."

Towards the top of Portland Whit Bed oyster beds are present and these have been examined by the Albion Stone Manager, Mark Godden. He has encountered these in the Jordan Mine, and demonstrated that they appear to cut down in an irregular manner. See the photograph above, taken in the mine. This feature is something which Mark has demonstrated over the last couple of years or so to many field parties that he has led in his mines. The oyster reefs, in addtion to oysters, contain the moulds of aragonitic bivalves which have been lost by dissolution. They may also contain some red alga - Solenopora.

These patch reefs can be seen, neatly cut through, in the Jordan Mine of Albion Stone. This mine was not in existence when the work of Fursich and his co-workers took place. The base of a reef can be seen in a photograph above. The relationship of the reefs to the Whit Bed (beneath) is puzzling. Are the reefs in channels, subsequently filled by the reefs? Have, instead, the reefs formed on a level sea-floor and then subsided into the originally soft Portland oolite sediment?

With regard to field exposures, Dr. Geoff. Townson, the Portland Stone specialist (see: Townson, 1975) has pointed out many interesting reef features in the Inmosthay Quarry complex, belonging to Albion Stone. Details can also be seen in slabs of "Shelly Whit Bed", i.e. the reef material, in the Albion Stone factory. Some example features in slabs are shown below.

Early cementation and erosion of patch reef material, Shelly Whit Bed slab, Portland Stone, Albion Stone Factory, Isle of Portland, Dorset, 29th March 2012

Penecontemporaneous clasts of bivalve-rich limestone, junction of Shelly Whit Bed and the Roach, Albion Factory slab, Portland, Dorset, 29th March 2012

Here in cut slabs of the oyster reefs or Shelly Whit Bed (upper part of Whit Bed), penecontemporaneous limestone clasts of cemented and bored Portland stone are seen (courtesy of Mark Godden).

Principal Framebuilders

Framebuilders of the Portland Freestone, Oyster Patch Reefs, proportions, after Fursich

The oyster Liostrea expansa, in a patch reef in the Portland Freestone of Inmosthay Quarry, Isle of Portland, Dorset, 29th March 2012

The main framebuilder of the reef is the oyster Liostrea expansa J. Sowerby. The red alga Solenopora 'portlandica' is most conspicuous because it is more striking and unusual than a Jurassic oyster, but actually the oyster shells are more abundant (Fursich, 1994). This oyster, Liostrea expansa is a thick-shelled oyster of medium size that grew in a somewhat cup-shaped form. It is larger than the dwarf Portland Group oyster Nanogyra nana and smaller than the flat triangular, Kimmeridge Clay oyster, Deltoideum delta. Although unremarkable in appearance, it is quite striking in the Portland Freestone because, like other oysters, it has a shell of bluish calcite and this has survived. Aragonite shells in the reefs have been dissolved long ago, leaving moulds.

Internal moulds of Plicatula from the Roach of the Portland Freestone, Isle of Portland, Dorset

Plicatula damoni is the second-most important framebuilding bivalve of the reefs. In the reef edge it is dominant and exceeds Liostrea in volume (Fursich, 1994).

Go back to top

QUARRIES - A:

Admiralty Quarries

(Originally Portland Freestone quarries for the Portland Harbour breakwater, but now a single, active, large and deep quarry for aggregate, into the Portland Cherty Series in the northern Isle of Portland, south of the Verne. Uses blasting and crushing.)
map reference: SY696728

Admiralty Quarries, Isle of Portland, Dorset, a general overview in 2011

The southeast corner of Admiralty Quarries, Isle of Portland, Dorset, shows a shallowing-upward carbonate-silica sequence deposited at the end of the Jurassic

This large working (in 2011) quarry is about half a kilometre southeast of the public car parks at New Ground or Verne Yeats. A public footpath to Grove passes the eastern side of the quarry. Since the quarry has been much extended its outline on old maps may not be accurate now.

The quarry has an old history because in the 19th century it supplied stone for the Portland Harbour breakwaters and thus the Admiralty naval base. The Roach was used on a particularly large scale for their construction. The breakwaters were planned in 1844 to shelter ships of increasing size and to form a strong naval base as a defence against France. By 1855 major progress was being made and 560 men were employed on the breakwater. Stone from the Admiralty quarries, worked by convict labour (the quarry is near the old prison), was deposited at the rate of 10,000 tons per week. The first stage was complete by 1867. There were forts at each end of the two initial sections and at the Nothe (Weymouth). A new section was built from the north side between 1895 and 1903 by civil engineering contractors.

Thus Admiralty Quarries originally were working the Portland Freestone, and as mentioned, the Roach in particular. Thus the Portland Freestone is missing over much of the adjacent area. The present quarrying much deeper and includes most of the Portland Cherty Series. This is crushed for aggregate, a more recent activity on the Isle of Portland, and one that now results in the excavation of large and deep quarries. Blasting regularly takes place and machines crush the rock within the quarry (see photograph).

Go back to top

QUARRIES:

Admiralty Quarries
- Portland Cherty Series - The Ladder Chert

The Ladder Chert of the Portland Cherty Series, Admiralty Quarries, Portland, Dorset, 2011

The Ladder Chert is a notable feature of the Cherty Series in Admiralty Quarries. This is a ladder-like development of chert in about the middle of the Portland Cherty Series, and is shown in a photograph above. It is best-developed in the southeast corner of the quarry but some is easily accessible near the northwest entrance. The chert is, in general here, the result of unmixing (i.e. diagenetic segregation) of silica from opaline sponge spicules of reniform geoditid type (Rhaxella). It is assumed that the chert was initiated as an opaline precursor but the details of the diagenetic history have not been firmly established. If the vertical chert is following joints it could be of various dates. Late Portland chert even in Tertiary fault planes is known at Dungy Head and elsewhere. The Ladder Chert is probably much earlier. It seems to be continuous with and therefore probably synchronous in origin with the bedding-parallel chert.

Go back to top

QUARRIES:

Admiralty Quarries
- Portland Cherty Series (top)- The Laevitrigonia gibbosa Bed

The location of the Laevitrigonia gibbosa Shell Bed near the top of the Porltland Cherty Series, Admiralty Quarries, Isle of Portland, Dorset, 2011

An interesting feature, well-shown in the eastern side of the modern and deep Admiralty Quarry, is the presence of a shell bed, about half a metre thick and almost at the top of the Portland Cherty Series (not to be confused with the Basal Shell Bed). It has conspicuous mouldic secondary porosity [i.e. moulds of originally aragonitic shells]. This bed has some similarities to the Roach at the top of the Portland Freestone but is much lower stratigraphically and it not associated with typical oolite. It is quite conspicuous because it is characterised by moulds of a gibbous "Trigonia", that is probably Laevitrigonia gibbosa. The stratigraphical location of the bed is easily found because there are two thick, massive chert beds below it and a thin, planar chert bed above it. It is near the top of the Cherty Series Cliff and below the old Portland Freestone quarried area.

This is certainly not the first discovery of the bed; it has been know since the 19th century, although not necessarily at this site. Aubrey Strahan in 1898 discussed the Portland Stone of the Isle of Portland. He commented on Isastraea in the Base Bed (base of Portland Freestone) and then gave (p.120) the following statement regarding the following statement:

"Next below [i.e. at top of Cherty Series] is a bed of variable thickness full of Trigonia gibbosa. In the Verne Ditch an exceptional thickness of nearly 20 feet [6 metres]of rock is assigned to this band and it resembles the "roach" except in containing Perna mytiloides." [no great thickness was found in Admiralty Quarries].

[Note: Trigonia gibbosa is now Laevitrigonia gibbosa; and Perna mytiloides is now Isognomon isognomonoides. However in British Mesozoic Fossils I. isognomonoides is given with the range: Bajocian and Bathonian. Palaeontological study is needed.]

If Strahan's comments are correct there is a remarkable facies change northward. This might be expected because that was the direction of shallowing. Probably a very shallow Portland facies, closer to Weymouth, is absent because of relatively recent erosion.

Laevitrigonia Shell Bed in the Portland Cherty Series, Admiralty Quarries, Portland, Dorset, 2011

Laevitrigonia moulds and other bivalve remains in the Laevitrigonia Shell Bed of the Portland Cherty Series, Admiralty Quarries, Portland, Dorset, 2011

The Laevitrigonia Shell Bed of Admiralty Quarries, has some interesting sedimentological features. The almost complete lack of compaction shows that the cementation was very early. However, it does not seem to show typical hardground features, although careful search has not yet been made. Thus the cementation seems to have been just under the sea-floor. A notable feature is that there is an apparent lack of later cement within the moulds that have been formed by dissolution of aragonite. This might suggest that the aragonite-dissolution process was late, probably post Jurassic (because in the early Jurassic some sparry calcite growth in pores would be expected from late Jurassic, early Purbeck uplift - see Fursich et al. (1994)). However, detailed petrographic data does not seem to be available at present and more study is needed (and comparison to Roach petrography).

The Laevitronia Shell Bed is very likely the remains of a shelly facies that originated in shallower water than the main Cherty Series facies of: "Fine shell sand and sponge spicules in lime mud matrix" (of Townson, 1975 fig. 5). It may represent a phase of sedimentation of "Shell sand area in front of ooid shoal" facies. This facies has a high density of bivalves and is bioturbated.

Go back to top

QUARRIES - A

Admiralty Quarries - Mammaliferous Drift

On the northern part of Portland at about 120m (the level of a widespread plateau on the Dorset coast) was the Portland Mammaliferous Drift (Prestwich, 1875). It occupied an irregular trough in the Purbeck and upper part of the Portland strata in the northern part of the Isle (Admiralty Quarries) and contained horse and elephant remains. Well-rounded and unusually polished pebbles occur in places at the base. These might suggest that this could have been a raised beach or an Eocene pebble bed (see further comments below). Above this level was red clay or loam passing into coarse loess. In places this deposit was full of angular debris from the Portland and Purbeck strata, together with "a considerable number of small blocks (some a quarter of a ton in weight) of the hard sandstone or sarsen-stone of the Lower Tertiaries." The sarsens were much worn and stained reddish brown, and sometimes blackened by manganese oxide.

With regard to younger clastic deposits, including pebbles and sarsen stones, above the Portland Stone it is tempting to make comparisons with Black Down, Hardy Monument and Valley of Stones area. Well-rounded pebbles occur there in the Eocene gravels. Manganese blackening is common at the boundary of Tertiary (acid) deposits and carbonate such as the Chalk at Ridgeway Hill. The height of Bincombe Down (155 m. in the Weymouth Relief Road) is not much greater than the original top of Portland (about 130 to 140 m), although the Hardy Monument area is higher. Thus the Eocene, rounded-pebble deposits (with jasper) of Bincombe Down might be indicative of a peneplain that once continued south to the Isle of Portland. These comments are only preliminary suggestions and the old literature needs further study.

Go back to top

Quarries - B

Go back to top

QUARRIES - B

Bowers Quarry and Mine (Albion Stone)
(west side of northern Portland, near St. Georges Church and Blacknor)

SY 682718

The Base Bed and the Whit Bed of the Portland Freestone at Bowers Quarry, Isle of Portland, 7th June 2008, with underground workings

Members of the OUGS in a mine of Portland stone at Bowers Quarry, Isle of Portland, 7th June 2008

A new mine into the Base Bed of the Portland stone is being cut at Bowers Quarry, Isle of Portland, 7th June 2008

These are old quarries, reactivated in the 1970s or 1980s and now a large feature with an advanced system of underground mining of Portland Stone.

See the website of Mark Godden on the topic of quarrying on Portland. In particular there is some detailed information and good illustrations regarding Bowers Quarry .

Go back to top

BOWERS QUARRY continued:

The Hard Slatt (Hard Cockle Member, Purbeck Fm.)

The Hard Slatt is the bed which contains dinosaur footprints at Coombefield Quarry. See the webpage: Dinosaur Footprints in the Purbeck Group of the Isle of Portland.

Moulds and casts of halite crystals from a salt crust, the Hard Slatt, Purbeck Group, Bowers Quarry, Isle of Portland, Dorset, 2012

A dinosaur footprint in the base of the Hard Slatt, Lower Purbeck Group, Bowers Quarry, Isle of Portland, Dorset, 2012

A dinosaur footprint, of Ornithopod type, was found in one of the blocks of the Hard Slatt (Hard Cockle Member of the Purbeck Group). The "cockles", Protocardia purbeckensis are present within the fill of the footprint, probably with the usual lagoonal ooids that characterise this bed. The main dinosaur footprint locality is at Coombefield Quarry. See the webpage: Dinosaur Footprints of the Isle of Portland.

Go back to top

QUARRIES - C

Go back to top

QUARRIES - C:
Coombefield Quarry (large quarries near Southwell)
(includes the former Suckthumb Quarry)

(SY 691703)

Coombefield-North-Quarry, Isle of Portland, Dorset, a general view in 2011

A major working quarry is that of Coombefield northeast of the village of Southwell. The quarry entrance is at map reference 691703 and from here it extends mostly in a northward direction to the east-west road of Weston Lane and not far from Perryield Quarry. To the northwest of Coombefield is the area of the old Suckthumb Quarry which is now filled in. The Ordance Survey Map shows that there is a public footpath through Coombefield quarry. The workings, though, are an area of high risk, not publicly accessible without permission and are strictly controlled by the quarry owners. There are hazardous working faces and heavy machinery in use and it is necessary to keep clear of these. (Please note that some of the quarries in Portland expand quite quickly and others are filled quite rapidly. Quarry ownership may also change. Thus readers in the future may find that the situation is quite different at the time they read this and, therefore, they should make their own enquiries if they wish to visit. )

Position of Hard Slatt in part of Coombefield Quarry, northern face

Hard Slatt in the northern part of Coombefield Quarry

Hard Slatt with herring-bone cross-stratification, northern part of Coombefield Quarry, Portland

Blocks of Portland Stone in Coombefield Quarry, Isle of Portland

Southwestern face of Coombefield Quarry, Isle of Portland

This quarry is of interest in having good sections of Portland Freestone from which large blocks are cut. Above the Portland Stone is a good succession of much of the Lower Purbeck strata.

Purbeck succession in the southern part of Coombefield Quarry, Isle of Portland

An isolated stromatolite from the Perryfield Stromatolite Bed at Coombefield Quarry, western side, Isle of Portland

The Purbeck succession shows the Caps and Dirt Beds in normal facies for the Isle of Portland. The Hard Cap has tree-holes, left from the decomposition of narrow and inclined tree-trunks. The Great Dirt Bed is well-developed and, as usual, large silicified tree remains are present in the quarry debris from this. Some very good stromatolites around tree remains were once present in the southern part of this quarry, but these have been destroyed by quarrying now. A notable feature is the presence of the dinosaur-footprint bed, the Hard Slatt of the Hard Cockle Member, which is well-developed here. At a higher level is the Perryfield Stromatolite Bed (well known in Perryfield Quarry and described by House (1968). The association with strata containing evaporites, and total lack of freshwater fossils, makes it probable that these stromatolites are of hypersaline origin, like most modern examples. A few metres above the stromatolites is a thin bed of brown calcareous marl that is a type of cargneule or gypsum residue bed. This is the equivalent of the Portland Alabaster Bed which can be seen from time to time in the west cliffs, in the Wallsend area. Like most Purbeck gypsum this is now secondary gypsum after anhydrite after primary gypsum. Evidence at the west cliffs comes from anhydrite relics and from pseudomorphs. There is probably other evaporite evidence here in the quarry, such as lutecite and, possibly, celestite, but the sequence has not been studied systematically in terms of petrography.

Go back to top

QUARRIES - C - continued

Coombefield North Quarry - more details

Travertine and small stalactites within a major joint, Coombefield North Quarry, Isle of Portland, Dorset, 2011

The Portland-Purbeck junction in Coombefield Quarry, Isle of Portland, Dorset, showing downward impaction of a stromatolite, 2011

A mass of silicified ostraods, Purbeck Caps, Coombefield Quarry North, Isle of Portland, Dorset, 2011

This remarkable oval mass of silicified ostracods was discovered by quarryman Charlie Wilkinson. He has placed it on display in his garden. It is a massive, unbedded and oval lump of extremely hard silica. With a hand lens the ostracods are obvious, especially on the outer margin, where the silicification is not so complete. The interior is effectively an almost solid chert. It is grey and granular though and does not resemble typical Purbeck or Portland chert. It does not show conchoidal fracture. The oval ostracod valves are paired. They are without rostrums, like the so-called "Cypris purbeckensis" typical of the hypersaline basal Purbeck facies (up to about 70ppt salinity - see West for details). There are few scattered paired bivalves of about 2.5 or 3 mm. length. They are thin-shelled. No gastropods were seen. There is no obvious evidence of compaction and it seems to be a product of very early silification of an ostracod bed that has not been appreciably reworked or damaged by major wave action. The silica has not been examined microscopically as yet, but there are numerous minute, reflecting quartz crystals.

The main conclusions are:

1. It is a silicified ostracod sediment from a low energy environment.
2. The palaeosalinity did not exceed 70 ppt.
3. There is no evidence of low salinity fauna (no low salinity gastropods and probably no charophytes).
4. The silicification was early.
5. It is abnormal for silicification of large oval masses of ostracod sediment in the Purbeck.
6. It is from the Caps but the exact horizon is uncertain (at least above waist level above the Portland and probably a little higher).

An isolated stromatolite of the type found in the Soft Cockle Member, Perryfield and Coombefield Quarries, Isle of Portland, Dorset

Stromatolites from the Soft Cockle Member of the Lower Purbeck Group, brown with bacteria or algal, Isle of Portland, Dorset

Isolated stromatolites occur in the Soft Cockle Member of the Purbeck Group in Perryfield Quarry and in the northern part of Coombefield North Quarry, which is nearby. At both these localities a relatively thick, for the Isle of Portland, succession of Lower Purbeck strata are present. They are not found far to the north or the south of this area because there is a thinner sequence of Purbeck strata remaining there. The isolated stromatolites are related to the thrombolites of the basal Purbeck but are better preserved because they are in a clay matrix. They contain small serpulid worm tubes.

As shown above, when the stromatolites are left out in the weather for a long period they acquire a brown organic coating. This is confined to the original stromatolite surface and does not occur on pieces of intervening limestone. In a sense the stromatolites seem to become reactivated!

Go back to top

QUARRIES - I

Go back to top

QUARRIES - I

Inmosthay Quarry (Albion Stone)

(central northern Portland, between Easton Street and Wide Street).

(See also - Albion Stone - above)

A notice at the eastern entrance to Inmosthay Quarry, Isle of Portland, Dorset, 2011

A large block of Portland Stone is lifted away, Inmosthay Quarry, Albion Stone, Isle of Portland, Dorset, 2011

Go back to top

QUARRIES AND MINES - J

Go back to top

QUARRIES - K

Go back to top

QUARRIES - K:
Kingbarrow (King Barrow) Quarries (northern Portland)
SY 693728

Recent stomatolites at Lake Thetis, Western Australia and a Jurassic stromatolite in the Purbeck Group at Kingbarrow Quarry, Isle of Portland, Dorset

Kingbarrow Quarries, old workings on the northern part of the Isle of Portland, Dorset

Lower Purbeck strata, including the Great Dirt Bed, as Kingbarrow Quarries, Isle of Portland, Dorset

Great Dirt Bed, Purbeck Group, at Kingbarrow Quarry, Isle of Portland, Dorset Stromatolites around trees , Soft Cap or Soft Burr, Kingbarrow Quarry, Portland, Dorset

Old pit in the Portland Freestone at Kingbarrow Quarry, Isle of Portland, Dorset

In the nineteenth century there was extensive quarrying in the northern part of Portland at the Kingbarrow or Kingsbarrow Quarries. These are situated south east of Verne Yeates, the viewpoint on the summit of Portland. The map reference is SY 691729. They are something of a maze of small deep excavations and backfilled walls of blocks, now much overgrown and degraded but not completely infilled. In recent years they have been used by young motorbike riders and many steep worn tracks. Now the old quarries are being converted into a nature reserved. Unstable piles of stone blocks are being fixed with bags of cement.

Much of the earlier descriptions and fossil material has come from Kingbarrow quarries. A consequence of this is the bed names for the Portland Stone best apply to this area. Elsewhere, as at Portand Bill, for example all the named beds are not recognisable because there are lateral facies changes. Note, incidently, that Stewards Quarry of the old literature (Howe, 1910), the quarry of Messrs Steward and Co, is usually grouped with Kingbarrow and was linked to the main part of Kingbarrow by an inclined plane (Strahan, 1898).

Portland and Purbeck at Kingbarrow

Howe (1910) in a textbook on building stones summarised the succession of the Portland Stone of the northern part of the Isle of Portland as shown in the accompanying diagram. The details, particularly the occurrence of the Base Bed Roach accord with those described for Kingsbarrow (e.g. Strahan, 1898). The diagram conveniently gives the sequence and quarrying terminology.

The following old description of the Kingbarrow section, made at the time when the quarries were working, is that given by Strahan (1898, p.115). See also Woodward (1895, pp 198, 262). It was measured in the company of Mr A.M. Wallis, by whom the quarrymen's names for the strata were supplied. Metric figures have been added and minor additions of explanation or terminology made for clarity (specialists should see the original).

Kingbarrow Quarries -
Based on old description - Strahan, 1898 and Howe, 1910, with some annotations by IMW

Platy or laminated limestone, broken and weathered ("shifting rubble") - 6 ft, 0 ins. = 1.83 m
Yellow Clay - 1 ft, 0 ins. = 0.30m.
13. Massive laminated limestone ("hard slate") - 4 ft, 0 ins = 1.2 m.
12. Hard streaked (laminated) limestone ("Bacon Tier") - 2 ft, 0 ins = 0.61m.
Greenish clay, about - 0 ft, 2 ins = 0.05m.
11. Fine-grained argillaceous limestone, drying very white; used for holystone (i.e. for scrubbing ships decks) - ("Aish Tier") - 2 ft, 0 ins = 0.61m.
10. "Tufaceous" (i.e. thrombolitic or stromatolitic) limestone used for building in the island, chiefly in chimneys ("burr") ( i.e. the Soft Burr or Soft Cap ) - 1 ft, 4 ins = 0.4m. [This is the horizon of the "Fossil Forest" with stromatolite mounds around trees. It is the same horizon as the Fossil Forest east of Lulworth Cove. See the illustration above.]

9. Dark carbonaceous clay with fragments of limestone (limestone pebbles) and wood ("top dirt bed") (i.e The Great Dirt Bed) - variable in thickness, 0 to 1 ft = 0 to 0.3m.
8. "Tufaceous" (i.e. thrombolitic or stromatolitic) limestone ("gristle"); in the lower part traversed by holes ("chaff holes") 2 inches (0.05m) to 8 inches (0.2m) in diameter and 5 ft (1.5m) to 6 ft (1.83m) long, sometimes branching and filled with fossil wood. The holes are generally nearly horizontal or slightly inclined ("top cap") (i.e. the Hard Cap) - about 8 ft (2.44m) or 9 ft (2.74m.).
Carbonaceous clay and gravel ("Lower Dirt Bed") - 3 ins (=0.08m.) to 6 ins (0.15m.).
7. Hard brown "tufaceous" (i.e. thrombolitic or stromatolitic) limestone about 1 ft (0.3m) to 2 ft (0.6m.), but very variable ("Skull Cap") - 1 ft, 6 ins = 0.45m.
Carbonaceous parting; sometimes a chert bed with ostracoda ("dirt") - (i.e. Basal Dirt Bed) 0 to 2 ins (= 0.05m). (Note that although the thin Transition Bed is not specifically mentioned it is probably under this)
6. Oolitic limestone, honey-combed by the empty moulds of "Trigonia", "Cerithium" (now Aptyxiella) etc. ("Roach") - 3 ft = 0.9m. (As Howe, 1910, noted this was used for heavy engineering works, in the harbour etc).
5. Oolitic limestone ("Whit Bed") - 5 ft = 1.52m. (Howe notes that this was also known as the "Top Bed of Freestone" or "Brown Bed", and it lies immediately beneath the Roach. The two beds are often literally one, and the separation had to be artificially made, the roachy portions of rock adhering to the freestone being chipped away. The bed is a fine-grained oolitic limestone, of a warm cream to pale brown tint when fresh, but becomes white on exposure. In a rather irregular manner it is filled with shelly detritus, which tends to make it harder than the other beds under the tool. )
One or two layers of chert ("the rising") - 0 inches (this is a local feature)
4. Oolitic limestone ("Bottom Whit Bed") - 3 ft, 0 ins = 0.9m. ( The Bottom Whit Bed was noted by Howe, 1910, as a particular feature of Stewards Quarry, Kingbarrow ).
3. Limestone with much chert ("flinty beds"), Ammonites giganteus (i.e. probably Titanites titan) - 4 ft, 0 ins = 1.2m.
Limestone with much chert ("Curf") - 3 ft, 6 ins = 1.07m. (Howe mentioned that the Curf, in different places with or without flints, is a band of poor stone which is waste)
2. Oolitic limestone with numerous casts of "Trigonia, etc ("Base Bed Roach") - 1 ft = 0.3m.
1. Oolitic limestone ("Base Bed") - 6 ft, 0 ins = 1.8m. (Howe mentioned that the Base Bed is a fine-grained oolitic limestone, paler in colour and softer than the Whit Bed and not so markedly oolitic).

Section continued in an inclined plane leading to the quarries of Messrs. Steward and Co.

Parting - 0 ft, 3 ins = 0.08m.
Hard limestone - 1 ft, 6 ins (=0.46m.) to 2 ft, 0 ins (0.6m.).
Limestone with chert ("chert beds"). About 8 ft (2.4m.) below the "Base Bed Roach" lies a limestone with interlacing threads of chert (the "Flint Bed") which runs through the whole island. - 55 ft, 0 ins = 16.76m. (part of the Cherty Series)
Evenly bedded limestone ("Flat Beds") - 2 ft, 0 ins = 0.6m.
Massive fossiliferous limestone with some chert - 12 ft, 0 ins = 3.66m.
Clay about 6 ft = 1.8m.
Limestone, seen to 10 ft, 0 ins = 3m.
End of main section.

Go back to top

- Kingbarrow Quarries continued - French Shells

Damon (1884) referred to a special fauna here.

"On the surface of the Whit Bed in the Kingbarrow quarries, and usually separated from the Roach above by a flint layer, are patches of a fine debris containing numerous minute but well-preserved shells, which I have not seen in other parts of the Island, neither do they appear to have been noticed elsewhere in Great Britain. They are not included in Mr Blake's table of the Portlandian fossils. On comparing these fossils with the species figured and described by MM. de Loriol and E. Pellat (1866) in their important work of [Monographie paléontologique et géologique de ] "l'étage Portlandien des environs de Boulogne-sur-mer," [Mém. Soc. Phys. Hist. Nat. Genève, v. 19] I recognise the following species not hitherto referred to Great Britain:-

Cerithium Carboeufi, De Lor.
Cerithium septemplicatum, Roemer
Delphinula vivauxea, Buv.
Nerita Micheloti, De Lor.
Odostomia jurassica, De Lor.
Orthostoma Buvignieri, De Lor.
Orthostoma granum, De Lor.
Pseudomelania paludinaeformis De Lor.
Serpula coacervata, Blum. [ the common serpulid of the Lower Purbecks and the German Serpulite]
Tornatina Oppeliana, De Lor.
Astarte
Cardita Boloniensis, De Lor.
Mytilus Moricanus, De Lor.
Spines of Echinidae
Spicules of Sponges"

As noted above, Damon (1884) referred to this assemblage as coming from the junction of the Whit Bed and the Roach. A dwarf mollusc assemblage, often silicified and associated with chert, occurs on the northern part of Portland at the top of the Roach, i.e. in the Transition Bed (junction of Portland and Purbeck). Was Damon correct regarding the horizon or did he see material attached to the Roach on loose blocks and think that it came from under the Roach rather than above? Confirmation of the horizon is needed.

Go back to top

QUARRIES - N

Go back to top


QUARRIES - N

Nicodemus Knob

(Small, old quarry, northeast Portland, near the cliffs and south of the Verne)
(SY 698732)
(including Grove, with early use for St. Paul's Cathedral, London)

Nicodemus Knob, on the east coast of the Isle of Portland, as seen in 1998

Nicodemus Knob, Portland, Dorset, seen on a grey and bleak day

Nicodemus Knob, Portland, Dorset, seen on its setting in an abandonned quarry, with the old prison visible in the distance

Climbing Nicodemus Knob, eastern Isle of Portland, Dorset, Petrostrat field trip, 7th September 2012

Nicodemus Knob, a section of Portland Stone, labelled, Isle of Portland, Dorset, 7th September 2012

Varied morphology of chert nodules in the Portland Cherty Series, Nicodemus Knob, Isle of Portland, Dorset, 7th September 2012

Nicodemus Knob, map reference SY 698732, is a conspicuous monolith in a Victorian Quarry on the cliff top on the northeast of the Island between the Verne Fort and the old prison. It was used for building the Portland Harbour Breakwaters. The stone is a relic of unquarried, nearly horizontal, Cherty Series stone left when the rock has been removed from around it. This later quarrying which left the monolith is within a very degraded and much older quarry dating from before 1700. The stone for St. Paul's Cathedral came from the old quarry here. You will notice that there is no Portland Freestone around the cliffs just here now. It has been quarried away for the London buildings. The quarrying is so old that there are drystone walls built on a base of Portland Cherty Series, as a result of the previous removal of the Freestone.

Old map of the Isle of Portland, Dorset, showing the site of quarrying for St. Paul's Cathedral, London

This map of 1710 shows that the only quarries present then were on the northeast side of the island. They coincide in position with the quarried area around Nicodemus Knob, northwest of the Grove. Notice the road down to the sea at King's Pier. At the present time there are vertical cliffs at the top and no easy place for a road to curve down the cliff. Compare with a modern map.

The quarrymen of about 1700 would not have used the Portland Cherty Series, which does not make useful building stone. The quarrying of this flinty limestone took place as a second phase of quarrying here round about the 1870s. It was convenient place for material for the Portland Breakwaters and near to the prison (presumably useful for labour).

Nowadays, the Portland Cherty Series is used for crushed stone and quarried in the large excavations such as Coombefield. In the past it was not quarried much because it was not useful for building purposes, unlike the good oolite of the Portland Freestone above.

For discussion of the origin of the name Nicodemus Knob see the webpage Nicodemus Knob Area, Portland, Dorset, by Geoff Kirby. He considers that the rock commemorates the activities of a certain Nick O'Demus in 1745.

Bioturbated Rhaxella biomicrite, with chert, of the Cherty Series, Nicodemus Knob, Isle of Portland, Dorset

This old quarry in the Cherty Series seems to have been a part of the extensive Admiralty Quarries which provided materials for the Portland Harbour Breakwaters. Adjacent to it, on the cliff to the east, is the Admiralty Incline. This was a long slope with railway tracks, down which railway waggons were lowered by galvanised steel ropes. These were continuous and two miles long. Stone quarried by the convicts was taken down the incline to Portland Nore at the start of the breakwater , sometimes at the rate of 2,000 to 3,000 tons a day (Legg, 1976 ). Much of it, though, was quarry rubble. The old incline, incidently, is now a road heading down to the former Naval base. In the photograph, in the distance is the old prison that provided the quarry labour. It is in use at present as a prison, although the main one is in the Verne Fort.

Rotary drilling taking place at East Weare, Portland, Dorset, on 13 April 2006

Drilling was seen to be taking place on the landslipped slopes below Nicodemus Knob on 13 April 2006. This is within the land belonging to Portland Port authority and formerly Naval territory. It is closed off by wire fences from public access. A medium-sized rotary drill was in use. The purpose of this is not known to the author at present. The borehole should pass through landslipped debris into the Upper Kimmeridge Clay. It should encounter the Kimmeridge oil shale a short distance below sea-level.

Go back to top

QUARRIES - T

Go back to top

QUARRIES - T

Tout Quarry
(old quarries in northwest Portland - Sculpture Park)

SY 686272

Tout Quarry is a maze of old quarry workings on the northwestern summit of Portland close to a good, look-out point or tout (tote) above West Weare. It is easily accessible from New Ground car park and the Portland Heights Hotel. It is notable for sculpture cut in Portland oolite.

Here is a modified version of Falcon-Lang's (1998) report on Tout Quarry (although the vertical log and aerial photograph are not given here - for these see the original report).

" Tout

This MRPZ is in the NW of the Isle and contains an old, disused quarry which is currently being used by the Portland Sculpture Trust. Only two bedrock outcrops are present, both of great geological importance.

Site Kl (SY 68627262)

This is a vertically-sided stack of rock, L-shaped in plan view (100 m by 25 m) which exposes a sequence spanning the Freestone Series to the Shingle [Slat] Beds. On the SW side of the stack, a bedding plane exposure of the upper surface of the Soft Cap occurs and exhibits a tree burr which has been cut in half by quarrying. Overlying Shingle Beds also yield occasional fish vertebrae.

Site K2 (SY 68647261)

This site is found on the SE side of the same stack of rock as in Site K1. Here a remarkable, in situ silicified tree trunk occurs rooted in the Great Dirt Bed; the best example of this rare feature on the Isle. The trunk is cover by an algal bioherm.

Site K3 (SY 68677273)

This is a vertically-sided stack of rock, square in plan view (approx. 25 m by 25 m) which exposes Freestone Series to Shingle Beds. The Freestone Series is exposed in a vertically-sided trench on the SE side and is poorly accessible. The rest of the sequence is accessible albeit with a small amount of climbing. The Basal and Lower Dirt Beds are particularly well-exposed here and some of the best examples on the Isle of 'branch holes' occur in the Top Cap on the SE face." [end of Falcon-Lang's report on Tout Quarry]

Strahan (1898) provides a section through "West Quarries". I suspect that these are the Tout Quarries. The desription of "Chaff Holes" in the Hard Cap or Top Cap corresponds with that of Falcon-Lang (1998).

Tout Quarries (West Quarries) - Strahan & Wallis Log, 1898.

(with some modifications and additions for clarity and with updating of terminology)

Lower Purbeck Group
(Caps, Dirt Beds, Broken Bed Equivalent, Cypris Freestones, Hard Cockle Members)

18. Marl with layers of limestone, top not seen
.................................................. 9 ft.
17. Hard limestone [the Hard Slatt or Hard Tier - the dinosaur footprint bed of Coombefield Quarry. Hard Cockle Member]
................................................. 3 ft.
16. Darkish clay and stone
.................................................. 2 ft.
15. Slatt - White laminated limestone [Cypris Freestones in part]
.................................................. 4 ft.
14. Yellowish-green clay
.................................................. 1 ft.
13. Slatt - Hard laminated limestone, contorted [ probably due to the former presence of evaporites] in Flew's Pits, one mile south of the West Quarries
.......................................... 3 ft. to 4ft.
12. Bacon Tier - hard streaked limestone [usually evaporitic]
.......................................... 1 ft. to 2ft.
11a. Clay parting
................................................ 2 ins.
11. Aish - fine-grained argillaceous limestone
.................................................. 2 ft.
10. Soft or Top Cap (Burr) - stromatolitic limestone
.................................................. 1 ft.
9. Great Dirt Bed - carbonaceous palaeosol with pebbles [in which the Purbeck trees are rooted. On an eroded surface].
..........from 1 to 12 ins ........ generally 8 ins.
8. Hard Cap - stromatolitic limestone with many casts of coniferous tree-trunks ("chaff-holes")
........................................... 6ft.to 8ft.
7a. Lower Dirt Bed, impersistent carbonaceous palaeosol
............................................... 3 ins.
7. Skull Cap - hard brown stromatolitic lst
......................................... 2 ft. to 3 ft.

Portland Stone (upper part) - beneath here

6. Roach - limestone full of moulds of Trigonia (Myophorella)
.................................................. 3 ft.
5. Whit Bed (the Upper Tier) - oosparite, the main quarried bed of Portland Stone. At the south end of the quarries this becomes nearly a "roach," (i.e. with shell moulds) and is not marketable. [ Damon (1884) noted that this bed is thicker in the western quarries than in the east, but the bottom part of this bed is softer towards the south. The stone of each tier is hardest towards the upper part.]
............................................ 12 ft.

(Downward limit of exposure in Tout Quarries, 1898.)

Succession continues down in the neighbouring area, the inclined plane of Kingsbarrow Quarries.

4. Bottom Whit Bed - oosparite limestone.
................................................. 2 ft.
3. Curf and Chert - limestone with layers of chert about 1 foot apart.
...................................................8 ft.
Base Bed Roach - Limestone full of moulds of Trigonia (Myophorella) etc.
............................................. 1 ft 6 ins.
Base Bed - fine oolitic limestone, oosparite.
................................................ 4 ft.

Go back to top

QUARRIES - W

Go back to top

QUARRIES - W
Windmill Quarry
(or Perryfield North, small quarry with succession up into the Purbecks, near Perryfield Quarry, (central Isle of Portland)

Windmill or Perryfield North Quarry, Isle of Portland

Windmill Quarry or Perryfield North is a northern and partly separate extension of Perryfield Quarry. It takes its name from the southern of the two old windmills to the southwest of Easton. The quarry is private property belonging to a quarry firm and you are warned that there is some risk of falling rock. Windmill Quarry is not at present in work and although it has an abandonned appearance it might be used again in the future. It consists of a partly-quarried base of Portland Stone with good cliff faces of the overlying Lower Purbeck strata. The basal Purbeck caps and dirt-beds are well seen. The caps are stromatolitic in part as usual and the Great Dirt Bed is quite conspicuous. For those interested in the Purbeck Group the most significant parts of the quarry are the Purbeck sequences from above the Great Dirt Bed. These are thin-bedded varied and accessible in exposures which are good. The sequence goes up from above the Great Dirt Bed through the Soft Cap (Soft Burr), the equivalents of the Aish and the Bacon Tier. The names of these two beds come from the Kingsbarrow area and they not identical here. Above these is the Shingle, a crumbly, laminated marl. Then then follows the Hard Slat, a hard calcarenite, which elsewhere on Portland contains dinosaur footprints at its base. The sequence which follows is mostly marl and clay with thin limestone beds and some chert. Most of this is equivalent to the Soft Cockle Member of the Lower Purbecks of the Dorset mainland. It is similar to the sequence described in (West et al., 1969). Some of the limestones are evaporitic and some contain the cockle - Protocardia purbeckensis. At the top of the exposed sequence is the Perryfield Stromatolite Bed, which has been described as of freshwater origin by House (1968) , although the present author considers this hypersaline because of its lack of freshwater fauna and association with evaporites. The stromatolites are isolated in marl and clay unlike those in the Purbeck Caps. They are best developed at the southern end of Windmill Quarry, almost directly at the connection to Perryfield Quarry. They are high and inaccessible in the cliff but fallen stromatolites can be found at the base of it. The succession does not continue much above this level. It is at near the middle of the Soft Cockle Member and small examples of the stromatolites occur on the mainland and can probably be correlated with this. The Portland Alabaster, the main gypsum of the Soft Cockle Member would occur just above but has been eroded away here. To see this and higher parts of the Purbecks it is necessary to go to the cliffs between Wallsend and Mutton Cove on the west coast of Portland.

Go back to top

QUARRIES

Withies Croft Wall
(Northern Portland)

Withies Croft Wall - Introduction

For more on Withies Croft Wall see Withies Web Page.

Withies Croft Wall in relation to SSSIs

Northern Portland with Withies Croft Wall

In the northern part of Portland, between the Verne Fort and Easton are the old Withies Croft Quarries. At the southeastern limit of these the old quarry face has been left until recently as a relatively narrow wall, referred to here for convenience as the "Withies Croft Wall". It has since been removed by quarrying operations. The general relationship of this to Sites of Special Scientific Interest (SSSI) in the north-central part of Portland is shown here (this small-scale map does not claim to show exact locations but is only illustrative of the general situation; more detailed information is available from English Nature). The description has been provided before it was removed because of a survey to make a permanent record that was commissioned by the quarry firm Albion Stone.

The old aerial photograph (1972), modified from an illustration of Morris (1990), shows the location of Withies Croft Wall in relation to the major landmarks of the northern part of the Isle of Portland. There have been many changes on Portland since this photograph was taken, in particular the development of a large and deep quarry northeast of the wall (to see details more clearly refer to Morris's book which contains another aerial photograph and 160 illustrations of the Isle of Portland in the past).

Withies Croft Wall - northeastern part

Withies Croft Wall - part

These photographs show the state of the wall on the 7th August, 1998, prior to the effect of road-making and quarrying activity . On top of this residual wall of Portland and Purbeck strata there was in the past also an artificial wall that marked the northwestern boundary of a convict prison quarry on the other side. There was in addition a lookout post. The remains of a lime-kiln associated with the prison quarry survives nearby.

The top left image shows the most northeasterly part of the Withies Croft Wall which still shows a clear section of the strata. The bank beyond is quarry debris. The road level is relatively high here and only the Whit Bed and Roach of the Portland Stone are visible, together with a basal Purbeck succession. The Purbeck Caps, Dirt Beds and some of the so-called "slatt" ("Cypris" Freestones) is exposed. Part of the Purbeck succession had been removed by the date of the photograph, leaving a surface at about the level of the Great Dirt Bed.

The image to the right of this is a continuation to the west.

Withies Croft Wall on 1902 map

Quarrying by convicts

Behind the wall were part of the original Admiralty Quarries in which convict labour was used to obtain stone for the breakwaters of Portland Harbour. The old convict workings were still there in 1902 as shown on this old map. Note the rail tracks and the positions of the look out posts. It seems that two such posts were originally on the Withies Croft Wall.

The lower photograph shows quarrying by convicts probably in the Admiralty Quarries. The old prison, seen in the background in a previous image above, provided labour on a large scale. The exact location of the quarry in the photograph is not known but it was undoubtedly in the area of the Withies Croft Wall, which, incidently, had tramway tracks like those shown here directly south of it. Perhaps, because of the direction of shadow the view is to the west. (This old photograph, is shown here with some minor retouching to improve clarity on the Web page. See copies of the original in Legg, 1976 and Morris, 1990. )

Go back to top

Quarries - Y

Go back to top

QUARRIES:
Yeolands Quarry
(eastern coast)

(SY 702718)

Yeolands Quarry in the eastern part of the Isle of Portland

Yeolands Quarry - northeast corner, Isle of Portland

This old quarry is situated above the east cliffs of the Isle of Portland, just south of the conspicuous building of the old prison, now a Young Offenders Institution. It is to the east of Easton and near Durdle Pier on the coast. It can be reached from the roads near the old prison, or by a short cliff-top walk north-east from Church Ope Cove. The large and deep quarry is abandoned but the adjacent quarry to the west, Broadcroft is still in some use. The north-northeastern face of the quarry has quite a clean, but partly overgrown, sequence of Portland Stone, both Cherty Series and Freestone. The Purbeck succession at the top seems to continue to the level of just above the Hard Slatt (Hard Cockle Member) but is somewhat degraded at the present.

The trace fossil - Thalassinoides, in Lower Purbeck limestone, Yeolands Quarry

Development and partiall filling of tree mould in stomatolitic limestone, Yeolands Quarry

The debris in the quarry is quite interesting. It is mostly from the Purbeck Group, particularly the "slatt" and associated marls and shales. There is some material from the Caps and blackened pebbles from the Great Dirt Bed can be seen, together with carbonaceous marl from this stratum. The Thalassinoides trace fossil is a system of crustacean burrows. These are very common in some marine formations, such as parts of the Portland Cherty Series and the Portland Sand. This only occurs at a few horizons in the lagoonal Purbeck Group and is rare in the lower part. It has been recorded by Falcon-Lang (1998) in the Lower Purbeck succession above the Hard Slatt, though, at various quarries on the Isle of Portland.

At the eastern edge of Yeolands Quarry near the cliff top and employed as a type of marginal barrier are many large blocks of stromatolitic (thrombolitic) limestone from the Purbeck Caps. Some of this is of typical Hard Cap type. In this there tree holes or "sandholes" where timber was encased in stromatolitic limestone and the wood subsequently rotted. These Hard Cap tree holes are usually of small diameter and at low angles, i.e. nearly horizontal. Here as in the Southwell area the holes have, in many cases, a partial filling developed after the decomposition of the wood. These incomplete fillings may consist of pelletoidal limestone, common at this level, or stromatolitic limestone or both. The remarkable aspect is that some Purbeck "stromatolitic" limestone was formed in partial darkness. This accords with the presence of "stromatolitic" material in a cylinder around the near-horizonal trees, and is thus not only above, but also beneath. Typical stromatolites at the present day are formed by Blue-Green microrganisms that contain chlorophyll. Thus an origin in considerable shade if not total darkness is puzzling and requires further investigation.

Go back to top


ACKNOWLEDGEMENTS

I thank particularly Mark Godden, the Manager of Albion Stone, for kindly giving access (on several occasions) and very informative guidance with regard to Bowers Mine and Jordan Mine, and the associated surface quarries of Inmosthay etc and the sawmills and factory belonging to Albion Stone. This has been very helpful. In particular he has drawn attention to the oyster reefs and their downcutting characteristics.

I am very much obliged to Dr. Geoff. Townson, the Portland Stone expert and retired oil industry geolgist. He is particularly knowledgeable and informative regarding Portland sedimentological structures, which, without guidance are very difficult to see in the quarries. Geoff. Townson has a specialist knowledge of the Portland Stone in the Isle of Portland, Isle of Purbeck, Vale of Wardour and the Boulonnais.

Charlie Wilkinson has kindly shown me various features in Coombefield North Quarry. Alan Holiday has provided photographs and information regarding conservation of Portland quarries, and this is much appreciated. I thank Gill Hackman for discussion in the field of historic aspects of the use of Portland Stone. Various research students and undergraduates have helped in the study of these quarries over the years.

Go back to top

BIBLIOGRAPHY AND REFERENCES

Go to Bibliography and References relating to the geology of the Isle of Portland.

Go back to top

|Home and List of webpages

Copyright © 2013 Ian West, Catherine West, Tonya Loades and Joanna Bentley. All rights reserved. Images and text may not be copied for publication or for use on other webpages or for any commercial activity, without permission. A reasonable number of images and text may be used for non-commercial academic purposes, including field trip handouts, lectures, student projects, dissertations etc, providing the source is acknowledged.

Disclaimer: Geological fieldwork involves some level of risk, which can be reduced by knowledge, experience and appropriate safety precautions. Persons undertaking field work should assess the risk, as far as possible, in accordance with weather, conditions on the day and the type of persons involved. In providing field descriptions on the Internet no person is advised here to undertake geological field work in any way that might involve them in unreasonable risk from cliffs, ledges, rocks, sea or other causes. Not all places need be visited and the descriptions and photographs here can be used as an alternative to visiting. Individuals and leaders should take appropriate safety precautions, and in bad conditions be prepared to cancel part or all of the field trip if necessary. Permission should be sought for entry into private land and no damage should take place. Attention should be paid to weather warnings, local warnings and danger signs. No liability for death, injury, damage to, or loss of property in connection with a field trip is accepted by providing these websites of geological information. No liability is accepted if this website is used beyond its academic purposes in attempting to determine measures of risk to life or property.

Go back to top

Dr Ian West, author of these webpages

Webpage - written and produced by:


Ian West, M.Sc. Ph.D. F.G.S.

.

at his private address, Romsey, Hampshire, kindly supported by Southampton University,and web-hosted by courtesy of iSolutions of Southampton University. The website does not necessarily represent the views of Southampton University. The website is written privately from home in Romsey, unfunded and with no staff other than the author, but generously and freely published by Southampton University. Field trips shown in photographs do not necessarily have any connection with Southampton University and may have been private or have been run by various organisations.