122 Prof. Hughes, On some Chipped Flints from [Mar. 9, 



Professor Prestwich 1 has given an instance of a sudden out- 

 wash due to heavy rain. In this way such superficial deposits 

 have often been carried down and deposited in stratified masses 

 hanging on the hill side. 



The relative levels of these gravels may be complicated by 

 contemporaneous or subsequent earth movements, but it will be 

 long before they lose the character they acquired from their 

 mode of origin, as they consist chiefly of surface-weathered 

 flints. 



These are all operations going on still, and the recent causes 

 and effects being obvious, we reason back by analogy to the ex- 

 planation of the more ancient results. Take such a district as 

 that between Six Mile Bottom and Linton. 



The higher ground, but not the highest only, is covered with 

 boulder clay. The chalk is rapidly perishing by subterranean 

 chemical and mechanical erosion. The upper chalk furnished 

 the flints which creep down hill by various processes, a large 

 proportion of them being at one time or another exposed on the 

 surface. Finally on the Six Mile Bottom side they creep down 

 the long "dry chalk valley" by Lark's Hall to the railway 

 station, carrying with them from above fragments out of the 

 Boulder Clay, and lower down incorporating the remnants of 

 terraces of river gravel of the age of the Mammoth and Tichorine 

 Rhinoceros. 



Over the undulating plateau on top, the stony patches creep 

 outwards and downwards as the inequalities admit of movement. 



Down the steep slope by Linton the debris slips fast, overlying 

 the patches of boulder clay and still older superficial deposits on 

 the brow of the hill and creeping out over the lower beds of 

 the chalk. If the outcrop of chalk is being eaten back, these 

 stony masses will by and by lie on isolated hills and old terraces 

 far out in front of the new chalk escarpment. 



In the country round Salisbury we find very similar conditions 

 prevailing and similar results following. There is an extensive 

 plateau, or rather " plain of marine denudation " over which there 

 are patches of Tertiary loams &c. resting, along the margin of 

 the Hampshire basin, on the upper or flint-bearing Chalk. 



On lower ground along the valleys there are terraces of Mam- 

 moth gravel. The " trail," consisting of the sweepings of ancient 

 and modern surface soils, has in one place crept off the chalk 

 on to the Tertiary beds, in another has travelled down and got 

 mixed up with the gravel of the old river terraces, which were 

 themselves largely made up of still more ancient surface debris, 

 with a few sarsen stones, black flint pebbles from the lower 



1 Quart. Journ. Geol. Soc, Vol. xlv. 1889, pp. 278, 279. 



