The Blackwater VuUcy, Knsej-. 17 



The base of the London Clay was met with at 295 feet, in 

 the shaft, with a westerly dip of 18 in 68. Boring soon after- 

 ward commenced in the Beading Beds, and at 343 feet a fault 

 was passed, and the London Clay reappeared. Its base was 

 again reached at 383, the Thanet Sands at 422, and the 

 Chalk at 477 feet. The Beading and Thanet Beds must be 

 inclined at high and varying angles, as at Witham (only two 

 miles off) they are only 27 and 24 feet thick respectively. 



We have here, therefore, a great wave, broken along the 

 crest, of the earth's crust, and, in a way that is most unusual, 

 determining approximately the form of the surface. In hard 

 rocks such a structure would most likely be along a valley, 

 with beds dipping into the hill on both sides. Even if a 

 stream had commenced a channel vertically over the present 

 course of the Blackwater, landslips would have perpetually 

 occurred from the south-east bank, till the stream was 

 shifted to the centre of the geological ridge. 



But in this case the surface consists chiefly of gravel, 

 without any bedding to produce landslips, and the under- 

 lying clay is a homogeneous mass, more prone to slipping 

 along its joint faces than the slightly-marked bedding- 

 planes, so that internal structure does not much affect the 

 physical features. 



But the coincidence of a very marked ridge wdth an excep- 

 tional undulation of the beds is suggestive of cause and 

 effect, and the draping of the hill with Glacial gravels, usually 

 only present at lower levels, and the absence from the crest 

 of any trace of Boulder Clay, which mantles round the foot 

 of the ridge to the N.E., seem to point to an elevation during 

 the Glacial period, whereby the crest of the ridge was raised 

 above the berg- covered sea, and a current produced at its 

 foot, which scoured away the gravel and dug into the London 

 Clay, leaving a channel to be afterwards occupied by the 

 Boulder Clay. 



On the subsequent emergence of the entire country, the 

 slope of the clay-bed determined the general trend of the 

 streams down to the N.W. foot of the ridge, and during the 

 cutting through of the estuary a lake was formed by the 



