A HISTORY OF BERKSHIRE 



extent show that a very long time has elapsed since the sea retreated 

 from the high ground of Berkshire. 



PEBBLE GRAVEL. The oldest gravel in this part of England consists 

 almost wholly of pebbles, hence the name Pebble Gravel. There are 

 small patches on the top of Ashley Hill and Bowsey Hill near Twyford, 

 and on the high ground above Streatley, which may belong to this 

 deposit or are perhaps mainly formed of debris from it. It occurs in 

 many places north of the river Thames. 1 



PLATEAU GRAVEL. Much of the high ground in east and south 

 Berkshire forms wide and flat-topped plateaux in which rain and streams 

 have carved out valleys. These plateaux are covered by sheets of gravel, 

 and at one time there was a pretty general opinion that the gravels 

 were of marine origin. The present tendency however seems to be 

 opposed to such a conclusion, and recent authors are inclined to regard 

 them all as gravels laid down by our rivers and streams and deposited at 

 various levels during the process of the formation of the present surface 

 features. 



The complete absence, so far as is known, of marine shells, etc., in 

 the gravels, and the existence of the clay with flints, support this view, 

 and the composition of the various sheets of gravel is also in its favour, 

 for it is not uniform as might be expected of a marine deposit, but 

 differs probably in accordance with the variation in the materials found 

 in the drainage areas of different rivers. 



Thus the gravels of the high ground near the Thames contain 

 pebbles and boulders of grey, pink and purple quartzite, which have 

 almost certainly been derived from the Triassic pebble beds of the 

 Birmingham district. They might have been brought by a river 

 flowing in the direction of the Thames itself, along the Cherwell and 

 Evenlode, though it is true that the Birmingham district is now in the 

 drainage area of the Severn ; but it is suggested that that river has in 

 course of time been gaining on and acquiring parts of the old drainage 

 area of the Thames. 



Then the sheet of gravels of Bucklebury Common, Greenham 

 Heath and of the great plateau between Aldermaston and Mortimer are 

 without the peculiar quartzites, etc., alluded to above, and contain only 

 such stones as might be derived from the drainage area of the Kennet 

 and its tributaries. 



Again, and still passing eastwards, the gravels of Finchampstead 

 Ridges and Easthampstead Plain are distinguished by the presence of 

 fragments of a peculiar chert and ragstone which has been recognized as 

 having come from the Lower Greensand of Surrey away to the south- 

 east, and though that country now belongs to the drainage area of the 

 Wey, it is suggested that it once belonged to that of the Lodden and its 

 tributaries, and that the Wey has gained on the Lodden, or rather on 

 the Blackwater, just as the Severn has gained on the Thames. 



The plateau gravels are mainly composed of flint from the Chalk. 



1 H. J. O. White, 'Westleton and Glacial Gravels,' Proc. Geol. Assoc. (1895-6), xiv. 1 1. 



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