350 PROF. PRESTwicn: ox the age, foematiox, and 



Bank. It appears to ascend to a level higher than that of the 

 railway, for it does not show in the cuttings beyond Combe Bank. 

 The only place where I have seen anything like traces of it has 

 been near Ivy House, one mile north of Westerham (430 feet), 

 where there is a sprinkling of drift similar to that of Chevening, 

 but there are no sections to prove it. This would give a gradient 

 from Combe Bank of about 32 feet per mile, while that from 

 Combe Bank to Dunton Green is equal to 35 feet per mile. This 

 gradient, if prolonged, would rise nearly to the summit-level of the 

 depression or gap on the north side of the Limpsfield watershed, 

 corresponding with the one before mentioned on the south side 

 of the summit-level (see fig. 5, p. 139). 



The various circumstances I have mentioned in connexion with 

 the brick-earth of Limpsfield Common, and with the Chevening 

 and Dunton -Green Drift, would seem to warrant the belief that 

 they are connected with a temporary return of glacial conditions *, 

 following, after an interval of milder seasons, the more polar cold 

 to which may be ascribed the previous vast giaciation of the dis- 

 trict — a giaciation that had already outlined the great physio- 

 graphical features of the country. It is difiicult to account for the 

 disturbed state and the peculiar condition of the brick-earth at Limps- 

 field, for the blocks of gravel rammed into the Gault at Chevening, 

 or for the presence in the same gravel of the Bed Clay with its flints 

 in a state so little altered, — otherwise than by the presence of ice 

 and snow, and by the removal of the original material from the 

 higher to the lower level in a frozen mass. A drift of that 

 character could not have been formed by river-action, as that 

 would show wear, and a structure in accordance with such action, 

 of which this gravel possesses none. 



It is also to be noticed that, after the gravel was pressed into the 

 Gault, the surface was apparently planed over, so as not only to 

 level any inequalities of the ground, but also to carry forward 

 some portion of the Gault, and spread it as a top layer, 1 to 2 feet 

 thick, over the whole (cZ', figs. 8, 9), in a way which suggests the 

 passage over it of a heavy weight. Another feature in connexion 

 with this drift is the number of flints here and at the other places 

 {Wray Common, near Beigate, for example), pitted or pock-marked 

 ■ — a condition owing not improbably to extreme cold. 



The prevalence of a temporary cold period might also serve to 

 explain the presence of some patches of angular Lower-Greensand 

 drift on the lower levels between AVesterham and Chipstead, and 

 the occasional occurrence of blocks of Lower Greensand of con- 

 siderable size. Mr. Topley notices several (one 17" X 8" x 4") near 

 Sundridge, and there used to be a block on the side of the road, 

 about J mile east of the Paper Mill. Lower down the valley there 

 arc several large blocks of Tertiary sandstone derived from the 

 strata on the adjacent Chalk plateau. Some of these lie in the 

 field on a low level between Otford and the brick-pits, and a block 



* I shall have occasion to adduce corroboraliTe evidence afforded by similar 

 conditions in the Thames '\''alley. 



