C— GEOLOGY 85 



not usually by British geologists, cannot have lasting value. In any 

 case, I hope that this exposition of the state of our present knowledge 

 and theories may have an historical use hereafter. 



Let me make a concluding summary by attempting a word-picture of 

 Pleistocene conditions in the British area in so far as they affected the 

 occupancy of the country by Early Man. We may assume that the 

 connection of the Early Pliocene sea of the south-east of England with 

 regions farther south was broken by an uplift of the Weald-English 

 Channel region, which resulted in the formation of the ancestor of our 

 present North Sea. In later Pliocene times, this sea became more and 

 more restricted as its limits were forced northwards. With the removal 

 of barriers to the migration of moUusca from the north, arctic species 

 found their way in increasing numbers into East Anglia. Geographical 

 and faunal changes about this time were so gradual and the effects of 

 penecontemporaneous erosion so marked that it is by no means clear 

 where we should draw the line between Pliocene and Pleistocene. In 

 our picture we must visualise at this time a land-area populated by plants 

 living under temperate conditions similar to those of the present day, and 

 drained by a great river that carried down the remains of southern ' warm ' 

 animals, such as the straight-tusked elephant, the hippopotamus and 

 leptorhine rhinoceros. Occasionally, however, there were also delivered 

 into the estuary the remains of cold-loving animals, while the sea with 

 which it was connected was the home of a cold moUuscan fauna. The 

 greater part of the east of England then seems to have been a land- 

 surface, although there are now but few definite traces of it available 

 for study. We have, however, the fissured surface of the Magnesian 

 Limestone of Durham, the ancient sea-cliff of Chalk at Sewerby, and the 

 surface of Pliocene deposits in Hertfordshire, Norfolk, Suffolk and Essex. 

 Ice began to gather in Scandinavia, and eventually found its way across 

 the North Sea ; its accumulation seems to have been accompanied by 

 a submergence of the land. Boulders of characteristic Norwegian 

 rocks were dropped on to the Scottish shores, particularly around the 

 Moray Firth and Orkneys, and the ice-sheet itself appears to have 

 impinged on the Durham and Yorkshire coasts. The evidence rather 

 suggests that, by the time the ice-sheet reached the position of the present 

 north-east coast, its force was spent, but its movement towards the south 

 was more definite, and, possibly behaving like the Great Antarctic Barrier, 

 it discharged its boulder-clay over the low ground of eastern Norfolk and 

 Suffolk. Icebergs may also have invaded the Fen country by way of the 

 Wash gap, dropping detritus even as far south-westwards as Oxford. 



In the long period of slow refrigeration which preceded this First 

 Glacial Episode, Early Man must have passed through the primitive 

 stages of his development as a tool-making animal, for the form and 

 technique which characterise the subsequent Chellian implements 

 could only have followed less easily-recognised efforts. The resemblance 

 in fashion of flaking and the repetition of form observed in the rostro- 

 carinate implements of the sub-Crag gravels is one of the strongest argu- 

 ments for their human workmanship. Also, the adherence to type bespeaks 



