glaciatipn, as having come from outliers of London clay, 

 nearly or quite denuded, which lay or lie at elevations well 

 above the 200 feet contour. The gravel spread of Dartford 

 Heath, Greenhithe and Swanscombe, contains many rolled 

 shells of Gryphaea ; on the Brent especially I found some 

 suspicious, clay like washed Boulder clay, and numerous 

 specimens of Gryphaea incurva and dilatata in a reduced 

 condition. There is, therefore, just a probability that the 

 clay lay in Kent. 



Whatever the origin of the Boulder clay, if we may 

 suppose that the upper level of the sea, at whose bottom 

 lay its near relation the Glacial gravel, extended upwards 

 to whereabout is the present 400 feet contour and the lower 

 level of the chalk-with-flints, we can picture the basins 

 of some of the rivers within the Weald as presenting some- 

 what the character of lakes in their deeper portions, and 

 I would refer some of the difficulties in tracing the course 

 of river denudation there, to this cause. In the Wealden 

 district, Southward, there is a plane which appears to lie 

 somewhere between the 400-500 feet contours, above and 

 below which a difference in the mode of denudation of the 

 district may be detected. No distinct river gravels 

 are found above it, while they are below. Above it 

 river valleys have been cut off, as in those of the 

 Darenth and Wandle, and the re-arrangement of river 

 basins appears to have commenced below it. The out- 

 lets of the Darenth and Med way at the chalk crest shew 

 a narrowing of the channel below it, and the difference in 

 breadth is marked by a terrace or shoulder, though this 

 may be due to a differing hardness of the chalk also. 



If the country had been excavated over any wide extent 

 of ground, before the rise of the sea level, as suggested 

 above, had ponded back the rivers, especially during a 

 period of great glaciation; the descent of snow and ice 

 from the hill sides, would push much of the old river gravels 

 into the water, -when some would be relaid, but some might 

 slide a short distance when near or just below the water 



