GEOLOGY 



The London Clay itself is as its name implies almost wholly clay 

 and of a very uniform character throughout, excepting near the top, 

 which is often rather sandy. It is practically impervious to water. It 

 extends over a broad belt of country from Windsor to Reading and 

 from that town south to the county boundary. 



West of Reading it is largely covered by the next formation, the 

 Bagshot Beds. 



Most of Windsor Park, Winkfield, Hawthorn Hill, Warfield, Bin- 

 field, Hurst, Arborfield, Shinfield, Swallowfield, Mortimer, Burghfield 

 and Beenham are on London Clay. It is but little obscured by superfi- 

 cial deposits. 



Its colour is dark, usually of a bluish tint, but near the surface of 

 the ground it is reddish or reddish-brown, the effect of the action of air 

 and percolating water. 



It contains layers of septaria or cement stones, i.e. nodules of hard 

 calcareous clay with divisions of calcite or aragonite. 



In the east of the county the London Clay is very thick. Several 

 wells and borings have passed through the whole formation. At Cum- 

 berland Lodge, Windsor Park, it was 314 feet in thickness, and at Ascot 

 Racecourse as much as 349! feet, but it gradually thins westwards. At 

 Wokingham it was 273 feet, Bearwood 256 feet, in the Burghfield 

 district it is only a little over 200 feet, and at Inkpen only 52 feet in 

 thickness. In all these cases the basement bed is included in the figures 

 given. It forms a stiff soil. 



At Bracknell, Wokingham and other places the clay is worked for 

 brick and tile making. Fossils are not common but occur in the sep- 

 tarian nodules. The bivalves usually have the valves united and are 

 not waterworn. Mr. Gardner considers that the climate was warmer 

 than in the Reading Bed period. The fossils are marine, and the extent, 

 thickness and uniform character of the greater part of the formation 

 suggest that owing to depression the sea water had encroached much 

 further up the estuary than in the time of the Reading Beds and even 

 than in that of the basement bed. 



BAGSHOT, BRACKLESHAM AND BARTON BEDS 



The three formations, Bagshot, Bracklesham and Barton, may be 

 taken together, for they are intimately connected with one another and 

 indeed are often all included under the general name Bagshot Beds. 



They extend over a considerable area in Berkshire. Sunninghill, 

 Ascot, Bagshot Heath, Easthampstead Plain, Sandhurst, Wokingham, 

 Sulhampstead Abbots, Ufton, Padworth, Aldermaston Park, Wasing and 

 Brimpton are on beds belonging to these formations. 



The surface of the ground is however to a large extent covered 

 with gravel; indeed it is to this fact that the patches of Bagshot Beds 

 owe their preservation. They are essentially soft formations, consisting 

 of sands with very subordinate beds of clay, and they have consequently 

 suffered great erosion from rain, streams, etc., so that though they 

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