THE THAMES PEOM GUILDEORD TO IfEWBUEY. 33 



The scarcity of chert and the abundance of small pebbles of quartz 

 are distinctive features of this gravel. The largest quartz -pebbles I 

 found measured 0-6 inch in length and weighed less than J oz. The 

 surface of the gravel slopes rather south of west, so that if this be 

 gravel of a river which flowed north earth-movements giving the 

 southerly dip must have taken place since the deposition of the 

 gravel. 



Although the l!^orth Downs are outside the area with which we 

 are now dealing, it may be well to mention that with this Upper 

 Hale gravel the Avriter would class that which is worked to the east 

 of Newlands Corner, 600 feet above O.D., which contains an abun- 

 dance of large rolled flints 3| to 4 inches in longest diameter, 

 together with subangular flints, flint-pebbles, chert, ironstone from 

 the Lower Greensaud, and small quartz-pebbles. The same gravel 

 is well seen at Woodcote Lodge, 678 feet above O.D., 1-2- miles N.W. 

 of Gromshall Station,^ and it may be that the drift of Well Hill, 

 Chelsfield," belongs to this stage. 



Class 2. Gliohham Ridges type. 



The gravels of this class largely consist of subangular brown 

 flints, but there is not the abundance of large flints which are found 

 at Upper Hale. In those pits men are constantly seen with ham- 

 mers breaking up the great stones, but in the other gravel-pits in 

 the Southern Drift, at least in the district with which I am dealing, 

 the hammer is not often used, and large stones are often thrown 

 aside and left in the pit. Besides subangular flints, gravels of the 

 Chobham Eidges type contain flint-pebbles, chert, and small quartz- 

 pebbles, and it is the presence of the chert and the abundance of 

 small quartz-pebbles which distinguishes them from gravels of the 

 Silchester type. On Sheet YIII. of the Geological Survey map. 

 Drift edition, a line of red patches is seen extending from Caesar's 

 Camp near Easthampstead in the north to the Fox Hills in the 

 south ; these patches clearl}^ represent what was once a great 

 plateau and originally part of the valley of a river flowing north- 

 wards from the Wealden country. Its southern end is drawn in 

 fig. 1 (p. 31) in outline to show its relation to the other gravels. 

 The surface of this great j^lateau, which will be referred to in this 

 paper as the Chobham Eidges plateau, is remarkably flat, as one may 

 gather from the following figures, which give the height above 

 Ordnance datum : — Easthampstead Plain 408 to 423 feet. Deer Eock 

 and Penny Hills 415 to 420 feet, Chobham Eidges 376 to 426 feet, 

 Fox Hills, Aldershot, 350 to 390 feet." 



On referring to Prof. Prestwich's section, fig. 2, it will be seen 

 that he brings Chavey Down into alignment with the Chobham 



1 See Proc. G-eol. Assoc. toI. x. (1887) p. 185. 



2 See Prestwich, Quart. Journ. Geol. Soc. vol. xlvi. (1890) p. 157. 



^ Descriptions of the gravels on this plateau by Prof T. Rupert Jones and 

 Dr. A. Irving will be found in Proc. Geol. Assoc, vol. vi. (1880) pp. 829, 438, 

 vol. viii. (1883) p. 161, and Quart. Journ. Geol. Soc. vol. xlvi. (1890) p. 557. 



Q.J.G.S. No. 189. D 



