C— GEOLOGY 87 



of the maximum glaciation ; and we assume that CheUian, and perhaps 

 Early Acheulian, Man retreated before it. The origin and provenance of 

 the few implements found in the Cromer Till and Chalky-Jurassic Boulder 

 Clay have been questioned ; if these implements demonstrate anything, 

 they show that the ice advanced over a Chellian land-surface. 



Milder conditions caused the recession of the ice-sheets of the Second 

 Glacial Episode, and the interglacial phase which followed was character- 

 ised by a pronounced amelioration of climate, and an aggradation of the 

 valleys. Little evidence is available for assessing the length of this 

 interval, but there is reason to suppose that it was shorter than the first 

 interglacial interval. Some diversions of drainage were caused in the 

 more hilly country during the retreat-stages of the ice, but the main 

 valley-systems were only enlarged and aggraded by swollen and detritus- 

 laden streams fed by the melting ice. The change to a temperate climate 

 is reflected in the return of Corbicula fluminalis to the British area, and 

 in the rich fauna and flora found in numerous lake-deposits ; it is not 

 surprising, therefore, that the evidence of the presence and activities 

 of Early Man at this time is most abundant and satisfactory. Acheulian 

 Man, in his middle and later stages of development, wandered over the 

 country and encamped near meres and rivers, doubtless hunting the 

 ' warm ' big game, such as the straight-tusked elephant, hippopotamus, 

 leptorhine rhinoceros, etc. He was succeeded as an occupant of the 

 area by Mousterian Man, whose remains are usually (but not always) 

 accompanied by evidence of colder conditions. Contemporary with the 

 Acheulian industry was the interesting Clactonian type of flaking which 

 may have marked a new human invasion from Central Europe. Climatic 

 oscillations occurred during this interglacial stage, as indicated by the 

 brief sojourn in eastern England of northern plants and animals ; also, 

 the presence of faceted pebbles in some of the gravels points to vigorous 

 wind-action, possibly connected with anticyclonic conditions during 

 the retreat of the ice. In the main, the English area stood at a lower 

 level than at present and, while the land oscillated in height from time 

 to time, the story is one of gradual uplift, by reason of which the streams 

 were able to erode their courses to lower levels, their braided sinuosities 

 being restricted at the same time within narrower valleys. 



From the general absence of Acheulian and Lower Mousterian imple- 

 ments in the north of England, even from the caves, we may conclude 

 that the area was inaccessible because of its covering of ice. The Second 

 Interglacial phase was brought to a close by cold conditions which, 

 if not excessively severe, were sufficiently cold to produce Coombe 

 deposits and Trail over the southern part of England, while a re-advance 

 of the ice took place farther north. The most noteworthy effects of this 

 re-advance were the production of the Cromer Moraine and the Upper 

 Chalky Drift, in which, it is claimed, Mousterian implements have been 

 incorporated from the pre-existing interglacial land-surface. The record 

 of this, the Third Glaciation of East Anglia, cannot be distinguished 

 with certainty farther north, but it may be represented by the Upper 

 Purple Boulder Clay of Yorkshire in those cases where two Purple Boulder 

 Clays with inters'ening sands and gravels can be identified. 



The ice that had gathered on the Southern Uplands of Scotland was 



