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PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



the Hog's Back and approach the depression in the Chalk-hills near 

 Farnham, than much debris is found occupying mounds on either 

 side of the river Wey. 



At this north-western angle of the great denudation — i. e. in the 

 tract lying between the forest of Alice Holt on the south-west, and 

 Farnham and the Hog's Back on the north-east, immense quantities of 

 angular and highly shivered chalk-flints are spread out ; not only over 

 the hillocks of Lower Greensand on the right bank of the Wey near 

 Wracklesham, but are distributed over the Gault of the broad and 

 elevated plateau of Alice Holt, where I long ago noticed them*. 



Copious accumulations of these are also exposed on the road 

 descending from Wracklesham to the Wey, and still better in the new 

 railroad cuttings from Farnham to Alton. The flints are tumultuous- 

 ly piled together and sharply fractured, and, mixed up with pieces 

 of chert and clinkers of the Lower Greensand, are lodged on the 

 irregularly eroded surface of that formation. Thence they extend 

 along the hillocks and slopes on each bank of the Wey eastwards 

 for the space of three or four miles. I cannot, in any way, separate 

 the flint-drift of Alice Holt plateau and Wracklesham from that 

 of the hillocks on the sides of the Wey, in which the remains 

 of fossil mammalia have been found ; for there is a perfect continuity 

 between all these detrital accumulations. Nor can I dissociate from 

 the same drift, the heaps of flint-debris and gravel which are spread 

 out northwards from Farnham over the surface of the clays and sands 

 of the western portion of the London Tertiary basin. For, as the 

 debris which has been translated to the surface of the older rocks on 

 the escarpment side of the chalk is purely local, so that which has 

 passed to the north has local distinctions only. Thus, to the north 

 of Farnham and the Hog's Back, we find not merely the broken chalk- 

 flints in the drift, as derived from the adjacent ridges, but also highly 

 rounded flints, all of which, like those of Patching on the South 

 Downs (p. 372), have been denuded from the pebble-beds of the lower 

 tertiary clays and sands, and are associated with some fragments of 

 the grey-wether grit. Both the latter have been abstracted from 

 the subjacent and denuded formations in situ. In proportion, in- 

 deed, as you recede northwards from the chalk of the Hog's Back 

 and North Downs, and descend over the tertiary clays and sands 

 ranging by Frimley to Bagshot Heath and the hills north and west of 

 Windsor, the angular chalk-flints are seen to become scarcer and the 

 rounded pebbles more abundant, the latter being derived from the ex- 

 tensive dismemberment which the tertiary beds have undergone as 

 well as the subjacent and flanking chalk-ridges. Wherever hills of 

 the London Clay have arrested these drift-accumulations, as around 

 Binfieldf, they are as tumultuous and unstratified as any described on 

 the external slope of the South Downs, and they lie at all sorts of alti- 

 tudes, from the banks of the Thames to the heights around Farnham. 



* Trans. Geol. Soc. Lond. N.S. vol. ii. p. 100. 



f In many parts of this gravel, where the oxide of iron prevails, the materials 

 have been so cemented as to form a very hard rock. This " rubble," which is the 

 equivalent of the ' Combe Rock ' of Sussex {anted), occurs also around London. 



