96 



PROCEEDINGS OF THE aEOLOGICAL SOCIETY. 



at a height of 140 feet, it is 

 only covered by 6 feet of 

 gravel, while in fig. 30 it is 

 covered by about 50 feet of 

 the Quaternary series. 



Pig. 31 is a drawing to 

 natural scale, showing the 

 relations of the Thanet 

 sands to the covering bed of 

 gravel, where these sands 

 have fallen into pipes in 

 the chalk. The Thanet 

 sands have not been faulted 

 by any general movement, 

 but have dropped down 

 where they have been un- 

 dermined by the removal 

 of chalk by chemical action. 



It would appear as if this 

 chemical action had been 

 contemporaneous with the 

 denudation of the Thames- 

 vaUey district by pluvial 

 and fluvial agency, and had 

 preceded the deposition of 

 the covering bed of sand 

 and gravel. The proof of 

 this is that the fissures in 

 the sand are filled by veins 

 of gravel from ^ inch to 1^ 

 inch wide to a great depth. 



When the sands fell by 

 gravitation into the great 

 pipe (A) , (which penetrates 

 the chalk 25 feet, and the 

 Thanet sands an equal 

 amount), they filled it up to 

 a height of 20 feet. This 

 must have left a large 

 funnel-shaped hole on the 

 surface of the sands. It 

 will be seen that, although 

 the gravel is only 5 or 6 

 feet thick over the undis- 

 turbed sands at B, it has 

 been able to fill a cavity 

 30 feet deep in the Thanet 

 sands and chalk ; and yet 

 the top of the gravel is so 

 smooth that no one could 



