454 MK. R, M. DEELEY ON THE PLEISTOCENE 



tocene epoch, regarded in the light of our -knowledge of earlier ice- 

 action in the same area, indicate that very important physical 

 changes must have taken place towards the close of the previous 

 epoch — changes which led to the advance of an ice-sheet from a 

 direction markedly different from aU previous ice-flows, and the in- 

 troduction of an entirely new series of rock-fragments into the 

 Trent basin. The earlier glaciers all originated in the Pennine or 

 other British hiUs, and spread their debris over the surrounding low 

 lands ; but during the epoch I am now about to notice, the ice 

 advanced from a north-easterly direction, and for the first time spread 

 over Central England the outcropping rocks it successively en- 

 countered. The Boulder-clay with chalk and flint thus spread over 

 the country has been called, from the immense quantities of Creta- 

 ceous rock it contains, the Great Chalky Boulder-clay. 



Although I have divided this epoch into three stages, I do not 

 mean to affirm that there is any break between them indicating 

 lapse of time. Indeed the deposits may be seen to pass without 

 the least unconformability one into the other. 



In West Staffordshire the gravels and sands frequently contain 

 fragments of marine moUusca, especially on the western side of the 

 watershed. The marine deposits with flint, in this part of the area, 

 probably represent the whole Middle Pleistocene series, including 

 the Great Chalky Boulder-clay. According to this view the latter 

 deposit was not formed in the open water then spreading over the 

 west of England. 



It is mainly, if not wholly, due to the introduction of Cretaceous 

 rocks into the Trent basin at this stage that it is possible to classify 

 the Boulder-clays and divide the deposits of the Pleistocene period 

 into distinct lithological groups. 



Although the peculiar character of this north-easterly ice-flow 

 has been noticed by many geologists, so far as I am aware, no one 

 has suspected that it formed an abnormal episode in glacial history. 

 Professor James Geikie, to account for 'the peculiar direction of the 

 ice-flow, has advanced the hypothesis that the Pennine glaciers were 

 brushed aside by the advancing Scandinavian ice, which, sweeping 

 over England from the north-east, distributed the flints and chalk 

 of Lincolnshire and Yorkshire over central England. Mr. Searles V. 

 Wood, on the other hand, maintained that the direction of the ice- 

 flow was due rather to a change in the inclination of the country. 

 The attitude I have assumed towards these two theories has been 

 dictated more by the actual succession of the deposits, as I have 

 found them in the field, than from any inherent weakness in the 

 theories themselves to account for the dispersion of the boulders 

 under certain conditions. Assuming that the Scandinavian moun- 

 tains existed in their present form in older Pleistocene times, how 

 was it that the glaciers of this early period from the Pennine Chain 

 were sufficiently powerful to entirely shut out from this part of 

 England an ice-flow from the north-east similar to the one which at 

 a later stage formed the Great Chalky Boulder-clay ? Again, the 

 occurrence of Middle Pleistocene gravel and sand, containing chalk 



