156 PROP. PRESTWICH ON THE AGE, TORMATION, AND 



North Downs, a spur of Lower Chalk projects forward. It presents 

 a compact even surface, merely covered by 1 foot of chalky soil, 

 and free from either of the rubble-drifts. The line between the 

 Chalk and the soil is perfectly sharp and clear. There is no passage 

 from one to the other. The surface-layer has the characters of a 

 ■wash — maybe a rainwash — the slope above being steep and abrupt. 

 This surface is such as might have been produced by ice-action, 

 though it is only by its rounded form and clean-swept surface that 

 we can judge, for of ice-marks on a soft Chalk surface there can be 

 none. This conjecture accords, however, with the supposition that 

 the Chalk-rubble cannot be due to surface decomposition, for were 

 it so it should exist here, whereas the position of the spur at the 

 angle of the two valleys is that where the denuding action of the 

 ice would be greatest, and the surface most likely to be swept bare. 



§ 10. The Alluvium and the associated Neolithic Implements. 



Of this last phase of the Darent Valley there is little to be said. 

 A small breadth of alluvial clay spreads over the bottom of the 

 valley (see Map, PI. YII.), and levels the inequalities of the under- 

 lying drift. The greatest expanse of this alluvium is between Otford 

 and Riverhead, but in general it is comparatively of little import- 

 ance. The clay is of a brown colour, and occasionally slightly 

 peaty, but there are no regular beds of peat, nor is the clay, which 

 is from 3 to 8 feet thick, anywhere worked, and little is known of 

 the underlying gravel and chalk debris. At Shoreham Mill the 

 latter was found to be about 8 to 10 feet thick. 



But although geologically unimportant, the large number of 

 Neolithic flint implements found on the surface of the adjacent 

 fields testify to the comparative density of the population during 

 the prehistoric epoch. Flakes, celts, scrapers, cores, &c. are com- 

 mon on the Chalk slopes and lower grounds. They are mostly rude, 

 weathered white, and iron-stained at the angles by the plough. 

 Only a very few ground and polished specimens have been found ; 

 arrow-heads are scarce, but a few highly finished specimens have 

 been met with. The district was evidently much frequented by 

 Neolithic man, as it had been previously by Palaeolithic man. This, 

 however, is a subject for the archaeologist. 



§ 11. On the Chalk Escarpment within the Darent District. 



Although the Darent district is of too limited extent to embrace 

 all the phenomena connected with the structure and origin of the 

 Chalk escarpment, it nevertheless presents a number sufiicient to 

 test the accuracy of the hypotheses that have been proposed in ex- 

 planation of this moot problem, and to show how far the facts we 

 have had to notice are in accordance with them. I do not, how- 

 ever, intend here to enter upon a full discussion of the subject, 

 which is one that requires a wider field of observation, but merely 

 to notice certain objections to both hypotheses that present them- 

 selves within the area of the Darent Valley. 



