Page:VCH Berkshire 1.djvu/52

 A HISTORY OF BERKSHIRE The urchins Echinocorys vu/garis and Micraster cor-anguinum are to be found in most pits in the Upper Chalk and also often occur in flints in the gravels. All the fossils of the Chalk are marine. Windsor Castle stands upon a mound of Chalk which is believed to be an inlier, 1 that is to say the Chalk projects through the Eocene Beds, and Mr. H. B. Woodward tells me it may be seen in the ice-house in the Castle grounds ; the relations of the formations are however greatly obscured by a thick covering of gravel and alluvium. Chalk has been extensively used as a building stone, and many churches are at least partially built of it. Mr. Whitaker remarks that in some old churches, as at Tilehurst and Sonning near Reading, there may be seen a variety of chalk with irregular veins of a dusky tint as in many marbles. He adds that he had not met with it in any section. 8 Chalk is also used as a dressing for the clay soils, and many of the pits in the county have been worked mainly for that purpose. It is the great water-bearing formation of all the counties round London, and the water is almost invariably colourless, palatable and brilliantly clear. 3 The full thickness of the Chalk is not found in Berkshire, possibly the highest beds were not deposited over this area, certainly great denudation took place before the time of the Reading Beds, the next over-lying formation in the district. In fact there is here a very great break in the geological succession and a considerable series of strata occur in Denmark, Belgium and France, and even in other parts of England, which are absent here. READING BEDS The Reading Beds are the oldest Eocene formation in Berkshire ; there are however older members of that series in other places, for not only the top of the Cretaceous but also the bottom of the Eocene is wanting here. The Calcaire de Mons of Belgium and the Thanet Sands of Kent and Surrey, for instance, are older Eocene formations than any we have in this county. Hence the Reading Beds lie upon a very greatly eroded surface of Chalk. A band of Reading Beds crosses the flat ground from Bray by White Waltham and St. Lawrence Waltham to Twyford, and then turns by way of Sonning to Reading. Most of the town between the London Road and Southern Hill stands on them as does Coley and the higher part of Castle Ward. The plateau of Tilehurst is formed of this formation with a capping of London Clay and gravel. A strip of Reading Beds runs along the sides of the hills by Engle- field, Bradfield, Bucklebury, and spreads out to some width at Oare. The bottom of the Kennet valley below the alluvium and gravel is mainly formed of Reading Beds from Theale to Newbury, from which 1 W. Whitaker, 'The Geology of London,' Geol. Survey (1889), i. 176. 8 'Geology of Parts of Oxford and Berks,' Geol. Survey (1861), p. 22. 3 'The Water Supply of Berks,' Geol. Survey (1902). M