262 NEOZOIC TIME. [CHAP. XIII. 



of the climate in that period, and there can be little doubt 

 that glacial conditions prevailed in high northern regions 

 while the Crags were being formed in the east of England. 

 The ice must have been creeping southward for a long 

 time before it reached the latitude of Norfolk and led to 

 the formation of the remarkable accumulations which suc- 

 ceed the Pliocene beds of that district. Again, it is cer- 

 tain that ice lingered in Scotland, and in the mountain dis- 

 tricts of England and Ireland, long after it had disappeared 

 from the southern part of our country. 



1. Stratigraphical Evidence. 



In our review of the Pleistocene period it will therefore 

 be best to consider the whole succession of deposits which 

 occur in different parts of our islands consecutively, so far 

 as that succession has been ascertained. 



Scotland. 



Glacial Deposits. Many attempts have been made to 

 classify the Boulder-clays and gravels of Scotland, but no 

 two writers seem to be quite agreed as to the precise se- 

 quence ; some still speak of the Boulder-clay of Scotland, 

 as if there were only one, and others are willing to believe 

 in any number of such clays if only they are separated by 

 fossiliferous sands or gravels. Mr. Jamieson, however, has 

 shown that there are at least two distinct Boulder-clays, 1 

 and from Professor James G-eikie's descriptions 2 we may 

 infer that there are at least three sets of Glacial deposits. 

 The oldest are Boulder-clays of the hard and compact kind 

 which is locally known as Till; the stones which they 



1 "Quart. Journ. Geol. Soc.," vol. xxi. p. 162, and vol. xxxviii. 

 p. 160. 



2 ' Prehistoric Europe," pp. 261 and 386 ; " Great Ice Age," second 

 edition, p. 216. 



