144 PROF. PUESTWICH: on the age, FOR>lA.TIOlNr, AND 



Below Farnini^ham, beds of j2:ravel arc more frequent on the right 

 bank of the valley, while the left bank remains bare until within 

 three miles of Dartford. On the hill above Dartford Powder Mills, a 

 tliick and far-spreading bed of gravel sets in ; it extends to the high 

 road and the Xorth Kent railway-cutting. The mean height of this 

 bed above 0.1). may be taken at 112 to 100 feet ; and as the distance 

 from Eynsford Mills is five miles, this is equal to a gradient of about 

 22 feet to the mile. On the whole, therefore, the gradients from 

 Limpsfield to Dartford show a remarkable agreement, although 

 owing to the few and distant points of observation between Brough- 

 ton Hill and Dartford, and the greater uncertainty of these levels, 

 the intervening gradients may require some correction. Enough, 

 however, is established to show that the fall of the stream of gravel 

 is continuous, and analogous to that of an ordinary river-bed. 



The gravel at Dartford forms part of the great sheet which ex- 

 tends westward over Wilmington and Dartford Heaths, and east- 

 ward to Stone and Milton Street, near Swanscombe. It is from 10 

 to 20 feet thick, is roughly stratified, and consists of subangular 

 flints, with a large proportion of Tertiary flint- pebbles, and 

 numerous worn fragments of Chert and Eagstone — some of which 

 are of considerable size. But in addition to the large contribution 

 brought by the old Darent from the Chalk and Lower-Grreensand 

 hills, there is in the gravel of Dartford Heath and Stone a certain 

 proportion of Triassic red quartzite-pebbles, white quartz, and other 

 old rock-pebbles (veinstone, granite, &c.) derived from Boulder-clay 

 series north of the Thames, which serve to connect this bed with the 

 great spread of High-level gravel of the Thames Yalley. 



From a consideration of the facts now described, there is reason 

 to conclude that the Limpsfield gravel must be correlated, not with 

 the High-plateau gravel with which it assimilates in respect to its 

 level, but with the Upper Terrace of High-level gravel of the 

 Thames, and therefore that it is of later Glacial or so-called 

 post-Glacial age. There are, no doubt, breaks in the sequence, but 

 allowing for the fall of a turbulent stream, the prevalence of a con- 

 siderable degree of cold, and the subsequent extensive denudation, 

 of which there is sufficient evidence, the separate outliers exhibit 

 so close a relationship that I cannot doubt their common origin. 

 The Palaeolithic implements also of the Limpsfield watershed agree 

 in their general characters with those which I designated temporarily 

 as the " Hill Group " of the Shode Yalley or the high-level river- 

 gravel, and not with the older group of the Chalk Plateau, or with 

 those of the lower levels of the Thames and Medway. 



§ 5. Contemporaneous Drift in the Cray Yalley. 



Another discovery of Palaeolithic implements bearing a general 

 resemblance to those of the Limpsfield gravel, and agreeing with it 

 in geological position, has recently been made by Mr. De B. Craw- 

 shay near Green Street Green, in the valley of the Cray. They are 

 spread over the surface of a gravelly field on the side of the lane 



