Page:VCH Berkshire 1.djvu/42

A HISTORY OF BERKSHIRE Further earth movements took place at the close of the Lower Greensand period, and the sea gradually extended until in Chalk times it stretched far and wide over south Europe. There was however still in all probability a land area to the west, including Cornwall, part of Wales and Ireland. 1 After the deposition of the newest beds of Chalk now remaining in Berkshire there is a very long break in our geological history, which can however be filled in by a study of the rocks in other parts of England, in Belgium and Denmark. Our next formation, the Reading Beds, records a time when, though sea water flowed over at least the south and east of the county, it was water of a great estuary and not of the open sea. The succeeding deposits of Eocene age are more marine in character taken as a whole, but land was never far off, and possibly they may even in a small part be of fluviatile origin. During or soon after the close of the Eocene period further great earth movements took place, and as the result of the consequent folding of strata the London and Hampshire Basins were separated from one another and Berkshire eventually emerged from the sea and has remained land until the present day. A list of works relating to the geology of Berkshire was compiled by Mr. W. Whitaker, F.R.S., and will be found in the Report of the British Association for 1882, p. 340. This list, as well as the 'Geology of parts of Oxfordshire and Berkshire' (GeoL Survey, 1861) by Messrs. Hull and Whitaker, and the 'Geology of the London Basin' (GeoL Survey, 1872) by Mr. Whitaker, have been largely used in the preparation of the present history. OXFORD CLAY As has been already stated, the Oxford Clay is the oldest geological formation which comes to the surface in Berkshire, and it forms a narrow strip of low-lying land extending from the river Cole to the Thames at the northern end of the county. Buscot, Eaton Hastings and Dencourt stand on it. It is a good deal hidden by Gravel and Alluvium, and is mainly grass land. It consists of dark-coloured, often shaly clay, with bands of sep- tarian nodules and sometimes a little clayey limestone. Its thickness has been estimated by Mr. H. B. Woodward at 450 feet, the lower part of which represents the Kellaways Rock of other areas. Carbonaceous matter, selenite and pyrites are common. It is a marine mud, and a large oyster (Grypbaa dilatata), a characteristic fossil, has been recorded from Fyfield Marsh. It is not a water-bearing formation. The Oxford Clay dips underground to the east and is covered by newer rocks, the first of which is the Corallian. For further details reference should be made to Mr. H. B. Wood- ward's monograph on the 'Jurassic Rocks of Britain' (Geol. Survey, 1 W. F. Hume, 'The Genesis of the Chalk,' Pnc. Geol. ASM. (1893-4), xiii. 211. 4