24 



section in the coprolite pits near Whitwell, and mentions most 

 of the kinds of rock-fragments found in the Boulder Clay and 

 Hill Gravels, especially noting the occurrence of nodules from 

 the Cambridge Greensand. He is inclined to think the Barn- 

 well Gravel older than that of Chesterton, and notices the 

 extent of the former towards the Railway Station. The account 

 of the Barnwell Gravel pit is mainly quoted from that of 

 Mr Seeley, some information about the evidences of Palaeolithic 

 man being added. 



Finally he notices the absence of the Lower and Mid-glacial 

 series in Cambridgeshire, and correctly states the relative age of 

 the Blue Boulder Clay, Hill Gravels and River Gravels. 



1876. In December 1875 Mr W. H. Penning read some 

 "Notes on the Physical Geology of East Anglia during the 

 Glacial Period," which were published in the Quart. Journ. Geol. 

 Soc. Vol. XXXII. p. 191. Mr Penning gives an explanation of 

 the behaviour of the Middle Glacial beds which he had been led 

 to adopt after personally surveying large parts of Cambridge, 

 Suffolk and Essex. He observes, as Mr Searles Wood had 

 done, that these Gravels and Sands are overlapped by the Upper 

 Boulder Clay which caps the Chalk escarpment and then 

 plunges down into the Cambridge valley. He regards this 

 valley as of pre-glacial origin, and as having formed a land- 

 locked inlet during the period of Middle Drift, whence gravel- 

 bearing currents were consequently excluded. 



He mentions three kinds of gravels as occurring within the 

 brow of the escarpment : (1) Recent valley gravels, (2) Some 

 patches of doubtful age but at high level, (3) An elongated 

 series of gravels and loams at a height of 20 to 60 feet above 

 the present river Cam, and in some parts distant from its 

 present course ; as these contain here and there recent land 

 shells, he concludes that they indicate an ancient course of the 

 Cam. His general conclusions may be stated as follows : 



(1) That we have evidence of but one glacial submergence 

 followed by a corresponding movement of elevation. 



(2) That there are no Middle Glacial deposits whatever 

 within the area of the Cam valley. 



(3) Tliat the surface of the Boulder Clay was eroded and 

 covered by gravel on emergence. 



