See S. S. Buckman, "The Kelloway Rock of Scarborough," Q.J.G.S., vol. lxix. (1913) p. 152; E. Neaverson, "The Zones of the Oxford Clay near Peterborough," Proc. Geol. Assoc., vol. xxxvi. (1925), p. 27; J. Pringle, "Geology of Oxford," Mem. Geol. Survey (1926), PP-
Corallian (from the prevalence of corals) may be used to de note the shallow-water phase separating the Oxford and Kimeridge Clays; this phase began, however, earlier in England than in most places on the Continent, where clays continued to be deposited until the close of the Oxfordian. The Corallian is here considered to begin with the important stratal break at the base of the Argovian, and to embrace the Argovian (from Argovia, Jura Mts.), Rauracian (from Rauracia) and Sequanian (Sequana =Seine) of Continental geologists. The shallow water Corallian includes sandbanks, shelly limestones and oolites, with coral reefs and subordinate clays. The coral reefs were all of the fringing type, rarely more than 20 ft. in thickness, and they grew at vari ous times and places, wherever conditions were suitable. Begin ning in Yorkshire at the top of the Oxfordian, where the passage up to the Corallian is gradual and complete, they continued on the Continent into Virgulian times, when Kimeridge clay was forming in England. The fossilized reefs form the rubbly limestones ("coral rag") and this type of rock was repeated at five successive periods in England.
The outcrop of the shallow-water facies is almost continuous from Weymouth to Oxford, and reappears in Yorkshire, in Suther landshire, and in the Kent borings. Between Oxford and York shire, with the exception of a local reef at Upware, near Cam bridge, the formation is represented by a deep-water facies, the Ampthill Clay, a dark clay with much selenite.
See J. F. Blake and W. H. Hudleston, "The Corallian Rocks of England," Q.J.G.S., vol. xxxiii. (1877), p. 26o; W. J. Arkell, "The Corallian Rocks of Oxford, Berks, and North Wilts," Phil. Trans. Roy. Soc., Series B., vol. ccxvi. (1927), p. 67.
(from Kimeridge or Kimmeridge, Dorset) is di vided into the Lower Kimeridgian or Virgulian (from the abun dance of the lamellibranch Exogyra virgule) and the Upper Kim eridgian or Bononian (from Boulogne, France). It consists typi cally of a dark-grey or black shaly and bituminous clay, with selenite and layers of septaria; the outcrop usually forms low lying pasture lands, such as the Vale of the White Horse, the Vale of Aylesbury, much of the Fens, the Vale of Lincoln and the Vale of Pickering. Part of the Lower Bononian is represented by a sandy facies in Wiltshire, Oxfordshire and Buckinghamshire. Coast sections may be seen at Kimeridge in Dorset and in Filey bay, Yorkshire, while the best inland exposures are in brickyards at Swindon, Culham, Oxford, Brill, Ely and Market Rasen. In recent years all the zones have been proved in the borings in Kent.
At Kimeridge the carbonaceous clay contains bands of highly bituminous shale, which was worked in the 18th century for the extraction of oil, tar and manure. It is still locally used as fuel,
but gives off sulphurous fumes. In Holworth Cliffe, Ringstead Bay, spontaneous combustion broke out in 1826 after heavy rain, and continued for several years.
See J. F. Blake, "On the Kimeridge Clay of England," Q.J.G.S. xxxi. (1875), p. 196; J. Pringle, "Geology of Oxford," Mem, Geol. Survey (1926), pp. 66-67.
(from the Isle of Portland, Dorset). In the type localities of Purbeck and Portland there is a gradual passage up wards from the Passage Beds of the Kimeridge Clay into the Lower Portlandian or Portland Sands, 115 ft. thick. The Upper Portlandian or Portland Limestones include (I) the Cherty Series, 6o-75 ft. thick, with very large ammonites; (2) the Freestones, 20-40 ft., extensively quarried as building stone; near the top is the "Roach" or Portland Screw bed, consisting largely of Ceri thium portiandicum and still larger ammonites. In the Vale of Wardour, the Portlandian reappears in much the same form. The most northerly occurrences of Portland rocks are at Swindon, Wilts, and from Shotover near Oxford to Aylesbury, Bucks. Here the Portland sands are missing, the limestones resting di rectly on a lydite remanie bed of the Kimeridgian. The Cherty series has dwindled to a single "Cockle bed," a few feet thick, overlain by thick yellow sands with impersistent hard bands called Swindon stone, representing the freestones of Dorset. At the top are some chalky limestones and a representative of the "Port land Screw bed" or "Roach." In Yorkshire a Coprolite bed at the base of the Speeton clay contains rolled Portlandian ammonites of Russian facies.
See Sir A. Strahan, "Geology of the Isle of Purbeck and Weymouth," Mem. Geol. Survey (1898), pp. 6o-71 ; C. P. Chatwin and J. Pringle, "The Zones of the Kimmeridge and Portland Rocks at Swindon"; Summary of Progress, Mem. Geol. Survey (1922), pp. 162-168; J. Pringle, "Geology of Oxford," Mem. Geol. Survey (1926), p. 77.
(from the promontory known as the Isle of Pur beck, Dorset), the highest member of the Jurassic system, con sists principally of freshwater lacustrine beds, indicating extensive swamps, which were sometimes invaded by the sea, sometimes elevated into land surfaces on which grew large "cycads" and co niferous trees. They show the transition from the marine Port landian to the Wealden, the lowest division of the Cretaceous. Freshwater Purbeck beds have not been recognized north of Ox ford; the marine equivalents are possibly present in the Speeton Clay of Yorkshire. The Purbeck Marble, which occurs near the top of the series, is a limestone almost entirely composed of the shells of the pond-snail Paludina carinifera; it has been extensively used since mediaeval times in the interior decoration of churches and cathedrals.
See Sir A. Strahan, "Geology of the Isle of Purbeck and Weymouth," Mem. Geol. Survey (1898), pp. 72-III.