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. 20
