71 



This old northward course of the river appears to have been 

 gradually silted up, a bank being probably formed by the gravel 

 brought down from the Linton valley, so that it was slowly 

 converted into a series of marshy pools, remains of which are 

 now discoverable over the surface north of Shelford, where 

 patches of whitish clay overlie the gravel and contain recent 

 shells in abundance, such as are now found in the pools on 

 Sheeps Green, 



In the meantime the chalk barrier on the west was gradually 

 overflowed and breached, the initial impulse being probably 

 given during some flood time, and the immediate result appears 

 to have been the production of a lake in the hollow where 

 Hauxton now stands, and the spreading out of gravel over its 

 bottom. For the drainage would at first be blocked by the 

 second ridge of Chalk Marl, which then in all probability 

 extended continuously from Harston to Trumpington, and the 

 waters would be ponded back until they could overflow at 

 Hauxton Bridge ; this they ultimately did, and by the deepen- 

 ing of this narrow outlet the lake has been gradually drained. 



Such I believe to have been the history of the gravels about 

 Little Shelford and Hauxton, which therefore belong to a 

 somewhat later period than those previously described, and may 

 be classed with the more recent gravel flats. 



This lowermost series of gravels is nearly continuous up the 

 valley to Linton, and small pits have been dug here and there. 

 Near Bartlow station there are pits showing about 10 feet of 

 gravel and loam, in which elephant tusks have been found, as 

 well as shells of the genera Helix, Pupa, Bithinia, and Succinea. 



Along the main valley of the Cam larger spreads of gravel 

 are met with, now on one side of the present channel and now 

 on the other, extending thus for a distance of 13 miles from 

 Shelford to beyond Newport in Essex. The principal pits along 

 this line occur at the following places. 



Whittlesford. East of the station, in gravel and sand. 



Little Chesterford. A large pit just south of this place 

 exposes about 30 feet of gravel and sand in horizontal layers. 

 Teeth of Elephas primigenius have been found here. 



Wenden. At pits near the river 15 feet of loamy gravel is shown, 

 from which elephant bones have been extracted. 



