72 



of the chalk valley at Croydon, and the extreme inland 

 verge of the spread at Dartford Heath. The upper gravels 

 of the Old Wandle at Norwood do not contain them, lying 

 at an elevation above their range, and being of a previous 

 age. 



The very high patches of Kingston and Wimbledon 

 have not yet been found to contain any mammalian remains 

 or flint implements. But the high level gravels of Dart- 

 ford do, as also do the high level gravels of Middlesex and 

 Essex, yet though the unfossiliferous condition of the high 

 level gravels West of Shooters Hill may be thought to 

 separate them from those of Middlesex, Essex and the 

 east, they do not appear to differ more than some parts 

 differ from other parts of those spreads known to be fossili- 

 ferous, so that I class all these as one. The constitution 

 of the material of the higher level gravels differs but slightly 

 from that of the lower ; the main difference being diminu- 

 tion vertically, i.e., in the lower terraces, of the proportions 

 of foreign pebbles, and in an Easterly and Southerly direc- 

 tion as the river gravels recede from the beds which yielded 

 them, as well as to the susceptibility of some rocks more 

 than others, to disintegrate by exposure. 



Although the gravels of the higher terrace do not shew 

 much evidence of glaciation during their deposition, yet I 

 have seen at their base on Dartford Heath and elsewhere, 

 detached masses of London clay of considerable size which 

 could only, I think, have been carried by ice. 



Below the level of about loo feet O.D. on the Kent 

 and Surrey side lies another terrace, whose continuity is 

 broken. On the North side, however, the high level 

 gravels have passed by gentle gradations, in some places 

 without a break, down to the lower terrace, although 

 occasionally a denuded space separates them. The differ- 

 ence on the two sides of the river, is the consequence of the 

 gentle abandonment of the Northern part of the river bed 

 for the Southern,, the Thames has always shewn a tendency 

 to hug the Southern hills and form a scarp. 



