GEOLOGY 



BERKSHIRE is in parts decidedly hilly, but nevertheless much 

 of the high ground takes the form of flat-topped plateaux or 

 rises with a regular and gentle slope ; indeed it might fairly be 

 described as a county of tableland in which long and deep valleys 

 have been carved out. The highest levels are on the ridge of Chalk 

 which crosses the county in a nearly east and west direction from 

 Streatley to Ashbury, it being in places over 800 feet above the sea, 

 but elsewhere the hills and plateaux rise little above the 400 feet 

 contour. 



The county is naturally divided into three very well marked dis- 

 tricts. They are indicated by colours or groups of colours on the 

 geological map, but are almost as clear on any map where the hills are 

 shaded or the contours marked. 



The first of these districts forms the northern end of the county, 

 and there a succession of Oolitic and Cretaceous formations cross the 

 county in bands, with an east and west trend approximately parallel to 

 the ridge of high ground already mentioned. These formations consist 

 largely of clay, though there are also sands and prominent limestones. 



The second comprises the central part of western Berkshire, 

 extending from the Wiltshire border to the Thames, and forming the 

 sides of that river's valley from Wallingford to Reading. The tract 

 included in the bend of the Thames between Twyford and Maidenhead 

 belongs mainly to this district, as also does the ground upon which 

 Windsor Castle stands. The geological formation is Chalk, and it 

 is wholly calcareous. 



The third district includes the south-eastern end of the county, most 

 of the area south of the Kennet and some tracts west of Reading and 

 north of Newbury. The geological formations belong to the Eocene 

 System, and are composed of clay and sand. The Chalk extends under 

 the whole of these formations, forming a hollow or basin in which they 

 rest, and this is the western end of the London Basin. 



In this third district therefore formations newer than the Chalk 

 form the surface of the ground, in the second district the Chalk is itself 

 the surface rock, and in the first formations older than the Chalk lie at 

 the surface. 



Speaking generally, we pass from newer to older geological strata 



