THE CAUSE OF THE GLACIAL PERIOD. 331 



temporary enlargement of the glaciers about their sum- 

 mits. 



Nor are we wholly without evidence that these read- 

 justments of land-level which have been carried on so 

 Vigorously since the middle of the Tertiary period are 

 still going on with considerable though doubtless with 

 diminished rapidity. There has been a re-elevation of 

 the land in North America since the Glacial period 

 amounting to 230 feet upon the coast of Maine, 500 feet 

 in the vicinity of Montreal, from 1,000 to 1,600 feet in 

 the extreme northern part of the continent, and in Scan- 

 dinavia to the extent of 600 feet. In portions of Scandi- 

 navia the land is now rising at the rate of three feet in a 

 century. Other indications of even the present instability 

 of the earth's surface occur in numbers too numerous to 

 mention.* 



But, while we are increasingly confident that the main 

 causes of the Glacial period have been changes in the rela- 

 tive relation of land-levels connected with diversion of oce- 

 anic currents, it is by no means impossible, as Wallace f 

 and others have suggested, that these were combined with 

 the astronomical causes urged by Drs. Croll and Geikie. 

 By some this combination is thought to be the more proba- 

 ble, because of the extreme recentness of the close of the 

 Glacial period, as shown by the evidence which will be 

 presented in the following chapter. The continuance of 

 glaciers in the highlands of Canada, down to within a few 

 thousand years of the present time, coincides in a remark- 

 able manner with the last occurrence of the conditions 

 favourable to glaciation upon Mr. Croll's theory, which 

 took place about eleven thousand years ago. 



* For a convincing presentation of the views here outlined, to- 

 gether with abundant references to literature, see Mr. Warren Up- 

 ham's Appendix to the author's Ice Age in North America. 



f See Island Life, chapters viii and ix. 



