INTRODUCTION XXXV 



reappear at a more abrupt angle, and then form the line of picturesque 

 hills of which Walbury is the highest point. These hills extend from 

 the Wiltshire border near Shalbourn to tlie spot where they leave 

 Berkshire for Hampshire, near East Woodhay. The Chalk is also 

 present in the south-east of the county from Sonning, on the banks of 

 the Thames, to Eemenham, Wargrave, and Maidenhead. It must be 

 borne in mind that the hills of Bowsey, Ashley, and Crazey, between 

 Wargrave and Maidenhead, are thickly capped with London Clay. 

 The chalk hill, on which Windsor Castle is built, is distinct from the 

 main mass of Chalk, being probably an inlying boss which owes its 

 present position to its being elevated by some disturbance. The 

 three outliers, which include the Wittenham Clumps, have been 

 mentioned, and there is an inlying patch near Hampstead Marshall. 



At the junction of the upper, more pervious portions of the Chalk 

 with the Chalk Marl, numerous powerful springs are thrown out, 

 which are largely utilized for the growth of watercress, as at 

 Ashbury. 



Along this line too the plentiful supply of water has determined the 

 site of numerous villages. 



Where the Chalk actually comes to the surface we find rolling downs 

 overgrown by short turf, which forms excellent pasturage. But over 

 a large portion of the county coloured as Chalk in geological maps and 

 where Chalk does exist at a moderate depth, the actual surface is over- 

 spread by a stiff red clay full of flints, known as ' Clay-with-Flints.' 

 There can be no doubt as to the origin of this clay. Surface water, 

 percolating through the porous Chalk, dissolves and carries away in 

 solution the carbonate of lime which makes up the bulk of the rock ; the 

 small amount of clayey matter, which Chalk contains, and the Flints 

 are insoluble and are left behind. The process goes on everywhere, 

 but along the steep slopes the resulting product is washed down by 

 rain ; it accumulates on the flatter ground. Deposits of sandy clay 

 suitable for brick-making, and hence called 'Brick earth,' are found 

 associated with the ' Clay-with-Flints.' They are probably rearranged 

 sands and clays belonging originally to outliers of the Reading Beds. 

 This * Clay-with-Flints,' where it is present, will obviously give to the 

 soil and what grows upon it characters very different from those which 

 prevail where the surface is the Chalk itself ; the land is much more 

 largely arable, and woods are frequent. 



The dry valleys in the Chalk country often contain a spurious 

 gravel made up of broken flints, and sometimes a thin bed of clay 

 spreads over these troughs. In such situations the silvery-leaved 

 Potentilla Anserina is often very abundant. 



By walking across the belt of Chalk from Wantage to Newbury, or 

 Uffington to Hungerford, or from Ilsley to Theale, the peculiar 



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