of Secular Changes of Climate. 375 



When wo consider how difficult it, must be to detect in the 

 drift covering glaciated countries even a relic of early inter- 

 glacial deposits, and when moreover we remember that it is 

 only within the past few years that geologists have begun to 

 bestow anv attention on the subject, it is certainly not sur- 

 prising that direct geological evidence of so few interglacial 

 periods has as yet been discovered. In England geologists 

 have, however, already detected evidence of three interglacial 

 periods with four or five ice-periods. In Germany, quite 

 recently, two interglaoial periods and three or more ice-periods 

 have been recognized by competent observers. In Denmark 

 there are four boulder-clays separated by intercalated beds of 

 sand and clay. In severely glaciated Scotland, where traces 

 of Cornier interglacial periods can hardly bo expected, there 

 have nevertheless been found in old preglacial buried channels 

 and other sheltered hollows three, lour, and in some places five, 

 boulder-clays, separated from one another by immense beds of 

 sand, gravel, and clay. Some of these beds are found to be 

 continuous for long distances. It is true that these intercalated 

 beds have yielded few or no organic remains, but it may well 

 be that further research will yet result in the discovery of 

 more abundant fossils; for frequently the beds in question are 

 too thick and too extensive to allow us to infer their subglacial 

 origin. They do not in such respects resemble the deposits 

 which have been accumulated by aqueous action under ice, 

 but have all the characteristics of deposits which have been 

 laid down in lakes and lacustrine hollows. As some have 

 already yielded organic remains, a more extended scrutiny 

 will probably lead to the discovery of similar fossils in those 

 beds which are at present believed to be unfossiliferous. 



Interglacial Periods less strongly marked in. Temperate 

 Regions than Glacial. — I quite agree with Mr. Wallace that the 

 interglacial deposits never exhibit any indication of a climate 

 whose warmth corresponded to the severity of the preceding 

 cold. This, however, cannot be urged as an objection, for it 

 is a result which follows as a necessary consequence from 

 theory. It theoretically follows that the cold of the glacial 

 periods will not only exceed in severity the heat of the inter* 

 glacial, but will also be of longer duration. During the glacial 

 periods extreme cold is the characteristic of the winters, which, 

 owing io the presence of snow and ice, only becomes mode- 

 rated, although, of course, considerably, during the summers. 

 But, on the other hand, during interglacial periods mildness 

 and equability of temperature rail km- than heat are the cha- 

 racteristics both of summer and winter. 



That the cold of the glacial periods must have continued 



