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Ch. X ] 



INTER-GLACIAL TERIODS. 



197 



which the lignite rests, and by the large size of the erratic 



superim 



-x- 



In England the lignite, or forest bed as it is called, of 

 Cromer, on the Norfolk coast, presents a singular analogy to 

 that of Diirnten above described. It contains in like 



main 



the cones of the spruce and the Scotch fir, and the seeds 



mammal 



in common with the Swiss deposit. It was also preceded 

 and followed by a period of greater cold. The antecedence 

 of a colder climate is proved by the arctic character of a large 

 proportion of the shells of living species included in the 

 marine strata of Chillesford, near Ipswich, in lat. 52° N., 

 which, according to the observations of Messrs. Prestwich and 

 Searles Wood, are more ancient than the forest or lignite 

 bed, and the fact is also confirmed by the marine shells of 

 like character and age found in a deposit at Bridlington, 



fc3 

 O 



in Yorkshire, lat. 54° 1ST. On the other hand, proofs that 

 the forest bed of Cromer was followed by an era of severe 



great 



cold, is shown by the fact that it underlies the 

 mass of glacial drift, in part unstratified, and containing 

 boulders and angular blocks transported from great distances, 



polished and striated surfaces. f 

 . We are by no means sufficiently advanced in our interpre- 

 tation of the monuments of the Glacial Epoch, and of the 

 long succession of events which mark its history, to be able 

 to affirm that the inter-glacial periods of Diirnten and Cromer, 

 above mentioned, were contemporaneous ; but they both of 

 them alike demonstrate that there were oscillations of tempe- 

 rature in the course of that long epoch of cold. There were 

 also great changes, as before stated, in the form of the earth's 

 crust, many movements of upheaval and subsidence, and many 

 conversions of sea into land, and land into sea, during the 

 Wacial Epoch. We are in danger of underrating the quantity 

 of time during which the cold prevailed ; because, in propor- 



• 



tio 



marks 



grinding action of the 



great 



antecedent glaciation. The 



ice-sheet which now envelopes Greenland illustrates this 



Process. Were that ice to n 



Antiquity of Man, pp. 212-218. 



f Heer, Urwelt dor Schweiz, p. 532. 





