338 MR. W. WJEITAKER ON A DEEP CHAlS^NEL OF 



This section has been taken to about the 200-feet contour on 

 either side of the valley, and it should be noted that, whilst the 

 boundary of the high mass of Glacial Drift just touches that con- 

 tour on the east, and then only just by the spot to which the 

 section has been taken, on the west that boundary is above the 

 300-feet contour, far beyond the limit of the section. 



Nature of the Channel. 



It may be well to notice three explanations of the channel that 

 certainly suggest themselves. These are disturbance, sinking-in of 

 the Chalk, and erosion. 



As to the first, there seems to be strong imagination wanted for 

 the acceptance of the idea of a fault of the throw and extent needful, 

 and that must have been brought about during or since Glacial 

 times. Moreover, there are no signs at the surface of such a fault, 

 which must affect the Chalk. The Drift beds, too, that fill the 

 channel are not such as occur on the higher ground around. 



On the other hand, Mr. In gold, to whom we owe our information 

 about the borings, asks " If the Chalk at Wenden has been ploughed- 

 out, how do you account for the soft white Upper Chalk with flints 

 being found at from 300 to 350 feet below the level of the same 

 kind of chalk at the outcrop near by ? It seems to me more like a 

 settlement." As, however, the Middle Chalk has a few flints in 

 part, there is some doubt whether Upper Chalk is present beneath 

 the thick Drift in the Wenden borings, though this division pro- 

 bably goes down some depth in that neighbourhood. 



To explain the occurrence of so deep a hollow over such a length 

 of country by sinking-in of the gravel from dissolution of the Chalk, 

 is open to the objection that the infilling Drift differs from that on 

 the neighbouring hills, which, too, in most cases comes near or close 

 to the borings. Deep pipes in the Chalk we know to occur, but 

 these are very different things. 



I can see therefore no other explanation than a cutting-out of 

 the channel by erosion of some sort, the effect being perhaps 

 strengthened by later dissolution of the Chalk, which might take 

 place more readily here than elsewhere. It is this explanation 

 only that gets over the difiiculty of the peculiar character of the 

 Drift in the channel. 



It would seem that the channel was cut out before the deposition 

 of the Boulder-clay over the higher ground, for we have no such 

 beds as those in the borings anywhere above the Eoulder-clay, and, 

 on the other hand, they are more like the loams, &c. that occur 

 beneath the Eoulder-clay elsewhere. The deepest boring of all, 

 too, at Newport, begins just at the base of the Eoulder-clay. 



Mr. Ingold thinks that the channel reaches northward to AVhittles- 

 ford, the loam of the deep Newport boring being like that at 

 Whittlesford Eridge, near the station. This would add about 5 

 miles to the length of the channel, making it II miles. It is to be 

 noted,, however, that on the Geological Survey Map (Sheet 47) there 



