94 



In the Brickearths of the Darenth, between Dartford 

 and Erith, beneath the wide spread of the underplight 

 and trail of the latest or surface glaciation, traces of 

 disturbance in the deposits filling the abandoned bed of 

 the old river may be seen at Crayford ; some feet down 

 [PL ii. Jig. 4), confused trail may be seen as it was 

 arrested while coming down the cliff or river bank, it 

 may be followed deeper into the stream as irregular 

 masses of tumultuous gravel, representing the trail on 

 land, which by their weight have in places denuded the 

 soft strata. This descent of trail, as gravel from the hill 

 above may be traced about 450 yards to the west of this 

 section, where the torn chalk and contorted gravel and 

 sand may be seen. [PL ii. Jig. 7.) The trail or flowing 

 soil on reaching the Old Darenth River was not always 

 washed away as gravel, but its appearance in the river bed 

 is somewhat different to that on land, due to the increased 

 freedom of its motion in the stream-bed. Its power of 

 pushing up the sand and gravel over which it passed was 

 greatly reduced, and consequently its U.P. there is very 

 slight. The stuff is to all appearances a boulder clay, and 

 differs from the underlying soils by the mode of mixture of 

 its component parts and its diflfering constitution, which 

 can be traced to the variations in thie strata composing the 

 river banks. It is formed mostly of gravel opposite those 

 that are gravelly, and of clay and sand opposite those of 

 chalk, and consists obviously of scrapings from a land 

 surface. In both kinds, chalk in fragments is found in it, 

 but the finely ground chalk has apparently suffered partial 

 solution, and some of it has since accreted into soft 

 cretaceous masses. In the central and other parts of the 

 stream the current was powerful enough to sweep the 

 boulder clay away into gravel, but in others it may stiJl be 

 recognised even as far from the cliff as 300 or 400 yards, 

 diflfering in composition and colour (grey) from the gravels 

 and sands. Nowhere is the layer very thick ; three feet is 

 the maximum I have seen. 



