66 Dr Marr, Submergence and glacial climates during the 



levels, and new deposits 4, 5, . . . (not shewn in the diagram) would 

 be banked against or laid down upon those formed during the 

 period of subsidence and general accumulation in tracts c and a. 

 It will be seen therefore that relative height of deposits above 

 the present river- level is not in itself a necessary indication of 



The geological surveyors gave the following classification of 

 the Cam gravels: 



r Lowest Terrace 

 Gravels of the Present River System I Intermediate Terrace 



[Highest Terrace 

 Gravels of the Ancient River System. 



I shall treat of three of these, leaving out of account the gravels 

 of the Intermediate Terrace, which I have not studied extensively 

 owing to poor and infrequent exposure of recent years. I shall 

 speak of the gravels of the ' Ancient River System ' as the Obser- 

 vatory gravels, those of the highest terrace of the ' present river 

 system ' as the Barnwell village gravels, and those of the lowest 

 terrace as the Barnwell Station gravels. The ages of these 

 deposits will ultimately be accurately determined by an exami- 

 nation of the fossil evidence, including implements of human 

 manufacture. So far, the evidence of this kind points to the 

 Barnwell village deposits being of two ages, the older formed 

 during the period of delta-growth, the newer during the period 

 of re-emergence and erosion. At the end of the period of delta- 

 growth, and therefore of an age intermediate between those of 

 the supposed two Barnwell village deposits, I would place the 

 Observatory gravel, and certain loams, to be referred to later, 

 and after all of these, the Barnwell Station gravel marking the 

 culmination of the period of re-erosion, for there is evidence of a 

 later period of sinking and deposit after this was formed. This 

 succession is represented in Fig. 2, which shews a section across 

 the Cam valley at Cambridge, before the edges of the valley sides 

 had been destroyed leaving the Observatory gravels as a ridge 

 with lower ground on either side. 



In the figure the terms Upper, Middle and Lower Palaeolithic 

 indicate the ages of the various gravels as inferred by me from 

 the palaeontological evidence. I am using the term Middle Palaeo- 

 lithic in the sense in which it was used by Prof. Sollas in the 

 first edition of Ancient Hunters as equivalent to Mousterian. 

 I believe therefore that the older Barnwell village gravel is pre- 

 Mousterian, that of the Observatory (in part at any rate) Mou- 

 sterian, and the newer Barnwell village gravel and that of Barnwell 

 Station post-Mousterian, the former being of earlier date than 

 the latter. 



Mr Jukes-Browne, in an essay on the Post Tertiary Deposits of 



■I 



