GRAVELS SOUTH OF THE THAMES FEOM GUILDEOED TO JSTEWBUEY. 39 



similar gravel, though it is true I found one chert pebble on a field 

 near the former place, and there is no good section in gravel at the 

 latter. At Shapley Heath, 319 feet above O.D., there is a patch of 

 gravel in which chert is very scarce, but the gravel differs from 

 that of Silchester, for it contains many small quartz-pebbles. 



There is a considerable spread of gravel on Burtley Heath, near 

 Hook, about 250 feet above O.D. It contains many large flints, 

 and a sample of the smaller material gave the following result : — 



a. Subangular flints 80% of weight, 



h. Flint-pebbles 11 „ 



c. Quartz 3 ,, 



d. A sandstone pebble and some irony pebbles 5 „ 



Of these the subangular flints no doubt came from the Chalk or 

 older gravels, whereas 6, c, and cl may all probably have come from 

 the Reading Beds. I am inclined to think that this gravel and 

 that of Mattingley have nothing to do with the Southern Drift of 

 the hills, but were brought from the Chalk country to the south at a 

 much more recent date. In any case all the materials occur in the 

 present drainage-area of the Whitewater, along whose valley this 

 gravel lies. 



The Silchester plateau is of great extent and varies from about 

 280 to 328 feet above O.D. The fields round the walls of the 

 Roman town are covered with gravel 321 feet above O.D. (see 

 sketch-map, facing this page) ; and at Mortimer Hill, 314 feet above 

 O.D., there are some pits about 3 feet deep with water at the bottom, 

 the Bagshot Beds on which the gravel rests being very clayey. 

 There are also pits on Burghfield Common, 305 to 314 feet above 

 O.D. The gravel appears to be unstratilied and 4 feet or so thick. 

 A sample of smaller material from the pit 314 feet above O.D. had 

 the following composition : — 



Subangular flints very much decayed and broken 89 % of weight. 

 Flint-pebbles „ „ „ 8 „ „ 



Quartz-pebbles ,, „ „ 3 ,, „ 



I found no chert on this plateau, and there are very few small 

 quartz-pebbles, one or two occurring here and there. Mr. J. H. 

 Blake found one at Mortimer Hill 1*2 inches long and over | oz. in 

 weight, and there are a few pieces of the flinty variety of sarsen- 

 stone mentioned by Prof. Prestwich.^ 



Across the River Ken net there is an extensive plateau, the greater 

 part of which is known as Bucklebury Common, 300 to 446 feet 

 above O.D. It is not mentioned by Prof. Prestwich, but appears 

 to be capped by a gravel of the Silchester type. There is a pit 

 close to the Union Workhouse, south of Bradfield, 310 feet above 

 O.D., which shows 10 feet of yellow and ochreous gravel, the lower 

 part of which is stratified. It consists of subangular flints and 

 flint-pebbles. I found no chert, no quartzites of the Glacial Gravel 

 type, and very few pebbles or fragments of quartz. The western end 



1 Op. cit. p. 162. 



