﻿22 ME. W. HILL ON A DEEP [Feb. I908, 



escarpment, which we may call the HitchinYalley. Like the 

 valley in which it occurs, the channel takes a north-north-westerly 

 direction from what is known as the Hit chin and Stevenage 

 Gap, out into the plain beyond the escarpment, from point to point 

 a distance of 7 or 8 miles. For the first 3 miles it appears to be 

 contained within narrow limits, persistent ridges of Chalk occurring 

 on each side, and it might almost be compared with a Chalk combe. 

 At Hitchin, after passing between two well-marked knolls, its 

 confines become less clear, and there seems to be some evidence of 

 broadening as it emerges on to the Lower-Chalk plain and leaves 

 the higher ground of the main Chalk-escarpment. 



The greatest depth to which the channel has been proved is at 

 Mr. Eansom's boring 68 feet below sea-level. If we may take the 

 well and boring in the northern outskirts of Hitchin as approxi- 

 mately correct, its bottom here is 24 feet above sea-level, at 

 Ickleford it is 29 feet, and at Holwell Bury 34 feet above it. The 

 boring of the Hitchin Joint Hospital Board, 3 miles south of 

 Hitchin, reaches Chalk 159 feet above sea-level : yet I feel sure that 

 this is not the centre of the channel, but on the western side of it. 

 And the fact that the borings may not be coincident with the centre 

 may account for the differences of depth at Ickleford and Holwell. 

 The channel cannot be due to any faulting of the Chalk, for the 

 outcrops of the Totternhoe Stone, the Melbourn Eock, and of the 

 Chalk-Bock, all occupy their normal positions on each side of it ; 

 the erosive action of running water seems to be the most reasonable 

 explanation of its formation. 



If the channel be due to the effects of running water, the question 

 naturally arises as to which way the current flowed. Are we 

 dealing with the effects of a ' consequent ' stream formed during the 

 first great uplift of the Chalk, with its water flowing southwards, or 

 with the effects of a ' subsequent* stream due to the gradual wearing- 

 back of the Cretaceous rocks with a current flowing northwards? 



If it flowed southwards, unless we conceive local earth-movements 

 of which there is no indication, the floor of the channel between 

 Dye's Farm and Langley Bottom, a distance of 650 yards, must be 

 at least as much below sea-level as at Mr. Ransom's boring, and 

 there would be a thickness of some 380 feet of Drift between the 

 two points — not perhaps impossible, though hardly probable. 



The course of the channel to the southward of this is determined 

 by ridges of Chalk which rise to the east and to the west, up to the 

 300-foot contour-line, and the only place where it could pass is at 

 Bragbury End, 3| miles east-south-east of Langley. Here bare 

 Chalk is seen on both sides of the valley of the Beane, very little 

 below the 300-foot contour-line, the space between the bare Chalk- 

 ridges being about 450 yards. 



Almost in the centre of this space is the house of Mr. Berger, and 

 I am informed by Mr. Milne, agent for the Earl of Lytton, that in 

 a well dug here a few years back, Chalk was reached within 50 feet 

 of the surface. I think that this conclusively proves that the 

 channel did not extend much farther south than Langley, and that 



