67 



the railway, chalk appears in the ditch, and thus the older gravels 

 are probably separated from the newer deposits in the low 

 ground to the east (see Fig. 7, lent by H. M. Geological Survey). 



Fig. 7. Section through the Trumpington gravels. 

 W. Nine Wells. E. 



a = lowest terrace. 6 = second terrace, c = highest terrace. (Z = chalk. 



The gravel pits marked on the ordnance map near Vicarage 

 Farm are ploughed over, and the next section to be found is at 

 the S.W. end of the cutting on the Great Northern line near 

 Shelford. Here soft white sand is exposed, covered in one place 

 with a bed of white marl, shells occur in the former, and are the 

 same as those found at Barnwell. 



Cyrena fluminalis. Helix ericetorum. 



Pisidium (amnicum ?). „ arbustorum. 



Bithinia tentaculata. „ hispida ? 



Valvata piscinalis. 



It is difficult to trace this series of gravels any further south, 

 but there is a patch capping the high ground midway between 

 Stapleford and Sawston that may possibly be of the same age, 

 and just north of Sawston the ridge bends eastward towards 

 Babraham, so that some of the higher gravels near Babraham and 

 Abington may belong to the same series. It is no easy matter 

 however to separate this set of gravels from the older series 

 previously described as crossing the country hereabouts, though 

 I think it would be possible to do so if accurate observations 

 were made of the heights of the different patches. 



In the main valley of the Cam I can point to no deposits of 

 this age, they have pi-obably all been swept down to lower levels, 

 for reasons given in the first instance. 



Neither have I seen any similar terrace of gravel in the 

 valley of the Rhee, which appears to be of later date than any 

 of the other tributary valleys. No beds of gravel occur along 

 the banks of the Rhee from its sources near Ashwell as far down 

 as Barrington, and I am inclined to think that this portion of 



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