440 



MR, E. M. DEELET ON THE PLEISTOCENE 





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According to this classification 

 the Pleistocene deposits fall into 

 three epochs, viz. Older Pleisto- 

 cene Epoch, Middle Pleistocene 

 Epoch, and Newer Pleistocene 

 Epoch ; each of these epochs is 

 susceptible of still further divi- 

 sion into stages, each stage indi- 

 cating very considerable changes 

 in the climate and geography of 

 the British Isles. Pig. 2 is a 

 diagrammatic representation of 

 their succession and general mode 

 of occurrence. 



The Boulder-clays of the lower 

 series, or Older Pleistocene epoch, 

 are tough, bluish or reddish clays, 

 chiefly made up of the subjacent 

 rocks or those immediately to the 

 north or west ; they contain frag- 

 ments of all the Pennine rocks. 

 Oolitic and Cretaceous debris 

 only occur in them in the ex- 

 treme east of England, where the 

 Boulder-clay approaches the out- 

 crop of these rocks. The boulders 

 are, in fact, such as would be 

 brought down by glaciers de- 

 scending the valleys of the Der- 

 went, Wye, and other northerly 

 and westerly tributaries of the 

 Trent, debouching into and 

 crossing the valley of the latter 

 river. 



The clays of the Middle and 

 N'ewer Pleistocene epochs, among 

 which is included the Great 

 Chalky Boulder-clay, ar^'charged, 

 unlike the earlier series, with 

 large quantities of flint and chalk. 

 In these deposits boulders from 

 the Pennine chain do not form, 

 except in the west, a large pro- 

 portion of the harder rocks. 



The beds associated with the 

 Boulder-clays consist of wide- 

 spread deposits of sand or gravel 

 formed during times of submer- 

 gence, or of fluviatile gravels 

 occupying terraces bordering the 



