INTERGLACIAL EPOCHS. 261 



conclusion as those suggested by the boulder-clay at the base of 

 the section. Once more a great ice-sheet enveloped the country 

 and rolled forward its bottom-moraine. Underneath this second 

 advance of the ice the loose superficial deposits which had 

 formed in the interval were demolished — only a few patches 

 having been here and there preserved. The section Fig. 8 shows 

 how the ancient lacustrine beds have been cut through and 

 the newer till rolled into the gaps and hollows made by the 

 ice-plough. 



In other cases we find beds of clay with sea-shells inter- 

 calated between a lower and an upper mass of till — the presence 

 of which in like manner compels us to infer that the accumula- 

 tion of boulder-clay was not continuous but interrupted by one 

 or more long pauses, during one of which a considerable sub- 

 mergence of the land took place. 



In England similar evidence is forthcoming. Thus in 

 Lancashire and Cheshire we encounter considerable deposits of 

 sand and gravel, containing sea-shells and other exuviae of 

 marine organisms, which rest upon and are covered by boulder- 

 clay. In other places, as near Hull, we see estuarine deposits, 

 from which remains of the Pleistocene mammalia have come, 

 occupying a similar position. It is well known, indeed, that 

 there are several distinct beds of boulder -clay visible in the 

 East Anglian districts, which are separated the one from the 

 other by intercalated deposits, some of which are unquestionably 

 of freshwater origin. Mr. S. Y. Wood jun. describes a succes- 

 sion of no fewer than four boulder-clays, which, beginning with 

 the oldest, are as follow : — 1, The Cromer clay ; 2, The Great 

 chalky ooidder-clay ; 3, The Purple clay of Holderness ; 4, The 

 Hessle clay. 



The oldest of these clays, that of Cromer, rests upon the so- 

 called " forest-bed " of Norfolk, associated with which have been 

 discovered many mammalian remains, including those of ele- 

 phant, hippopotamus, horse, cave-bear, urus, Irish deer, and 

 many other cervidse. The fauna is remarkable as showing a 

 commingling of Pliocene and Pleistocene species. Thus we 



