66 



gravel, sand and loam ; the depth of these deposits near the 

 goods-sheds is said to be about 16 feet, but opposite the main 

 platform it is not more than 10 or 12 feet, and along the 

 Newmarket line it shallows to 7 feet, and was seen to rest upon 

 an irregular surface of stiff grey marl (probably the Chalk Marl 

 in situ, though containing impacted sand and pebbles). 



In the cutting near Polecat Farm the gravel is found again 

 and thus caps the highest part of the ridge overlooking the old 

 Cherry Hinton mere ; at the time therefore when the river ran 

 at the height indicated by this terrace or ridge, the mere could 

 hardly have been in existence, and its site was probably occupied 

 by ground that sloped upwards toward the Gog-Magog hills of 

 that period, the lower spurs of which have so far receded in the 

 interval between that time and the present, as to allow of the 

 formation of the mere. 



The Barnwell terrace is here about half a mile wide, and is 

 separated from the lower terrace on the west by a strip of chalk ; 

 southwards the terrace declines gradvially towards Brooklands, 

 and the beds have been washed down into the newer gravels, 

 which are here banked against the older series. 



The southernmost pit is situated in the angle between the 

 railway and the Hills Road, and shows from ten to six feet of 

 sandy gravel, with a band of marl near the bottom. The 

 ballast pits between the railway and Brookland Farm expose 

 about 8 feet of sand and gravel, resting on Chalk Marl. 



Having now described the position, character and contents 

 of the Barnwell gravels, it will be sufficient to trace their 

 continuation southwards. 



Crossing the shallow valley through which Vicar's Brook now 

 runs, and which we shall find to have been the course of the 

 Cam at a subsequent date, the higher series of gravels are 

 continued by Trumpington ; gravel and sand to a depth of 16 or 

 20 feet underlie the greater part of this village, but thin out 

 towards the church \ 



The railway cutting between the branching roads south of 

 Trumpington intersects this ridge of gravel, which appears to 

 thin out both eastward and westward, for near the 28th mile on 



1 The Rev. O. Fisher informs me that a tooth of ElepJias primigenius \y&3 

 found iu sinking a well at the Vicarage. 



