DRIFT-STAGES OF THE DARENT VALLEY. 149 



The ground is nearly level, and from 320 to 340 feet above O.D., 

 or about GO feet above the Darent at Sundridge, with a slight incline 

 southward, succeeded by a more rapid fall as we approach the river. 



The gravel lies in pockets and troughs, having a general strike 

 towards the north-east and south-west, and the line of separation 

 between the Gault and the gravel is clean and sharp. J^o loose 

 stones penetrate the Gault. It is as though the gravel had been 

 pushed bodily into the clay, which presented on the steep sides of 

 the pockets strongly marked slickenside-surfaces with the striae 

 directed downwards. Had the cavities been formed by running 

 water they would have inosculated one with another. But such is 

 not the case. Each seems separate and independent, and formed 

 by a process of punching, which could only be produced by force or 

 pressure, such as might be caused by a weight of ice or snow. 



The composition of the gravel is also exceptional, many of the 

 flints being of large size, perfectly angular, and identical with those 

 in the lied Clay-with-flints on the summit of the escarpment, 

 which rises at a short distance beyond ; while adhering to their 

 interstices was some of the same lied Clay. Besides these, there 

 were a few Tertiary flint-pebbles, which also are common in places 

 in the Eed Clay-with-flints, but no Lower-Greensaud debris. There 

 seem to be, therefore, grounds for supposing that this drift-bed has 

 been derived directly from the bed of Eed Clay on the escarpment 

 above. 



!N'ear the outlier of Limpsfield gravel on Sundridge Knoll, but 

 100 feet lower, there is another bed of gravel capping a low hill 

 at the level of 300 feet, and composed in great part of Lower- 

 Greensand debris, Tertiary flint-pebbles, brown-stained flints, and 

 with comparatively few white subangular flints. Whether this 

 represents the southern or Lower-Greensand border of the Cheven- 

 ing gravel stream, or whether it belongs to a subsequent stage, I 

 am unable to say. 



From Dun ton Green, the Chevening Drift apparently sweeps 

 round the eastern side of Broughton Hill by Rye-House Farm, but 

 no sections are exposed. On the slightly rising ground J mile 

 S.W. of Otford, and about 20 feet above the Darent, or 220 feet 

 above O.D., a coarse unstratified gravel, 4 to 5 feet thick, possibly 

 of this age, or a stage newer, is worked. It consists of : — 



1. Angular and subangular white flints, mainly. 



2. Some Tertiary flint-pebbles. 



3. A certain proportion of subangular Chert and Ragstone. 



4. A few dark brown subangular flints. 



The whole confusedly heaped together in a slight matrix of 

 reddish-yellow clay and loam. This bed, which reposes on an 

 uneven surface of Gault, is, however, on a lower level, and contains 

 more Lower-Greensand debris than at Dunton Green ; but this 

 may be due to a more rapid gradieut, and to the junction of the 

 eastern branch of the vallej' with other tributaries from the Green- 

 sand Hills (see Map, PI. YII.). 



Nor is any bed of this age clearly seen to the west of Combe 



