268 CLIMATIC CONDITIONS OF THE GLACIAL EPOCH. 



Thus prepared fur the continuance of our investigation by a knowledge 

 of the manner in which ice and snow are now distributed, and by a demon- 

 stration of the fact that tlie play of forces on which this distribution depends 

 is so delicately balanced that scarcely perceptible variations in their relative 

 preponderance do bring about results of magnitude, we shall proceed to the 

 next branch of the inquiry. Here we shall pass in review the most impor- 

 tant of the facts connected with the Glacial epoch. In the course of this 

 review the writer believes that it will be shown that if ice has formerly 

 extended over certain regions M'here now neither snow nor ice has any 

 permanent lodgment, these areas were of but small size, as compared with 

 the entire land surface of the globe, much the larger part of which remained 

 entirely unaffected by this abnormal glacial development. Such being the 

 case, it seems to follow, as a matter of course, that the phenomena of the 

 Glacial epoch, being local in character, have to be accounted for by combina- 

 tions of local causes, and not by a general one. After learning something 

 of the conditions requii'ed at the present day for the formation of glaciers, 

 the reader will, it is hoped, be prepared to follow the author in his attempt 

 to apply those conditions to the phenomena of the Glacial epoch, and to 

 show that to explain these it is proper to call in the agency of causes which 

 now produce results of a similar character, although perhaps, for the same 

 region, not of the sauie order of magnitude. In short, for each formerly 

 glaciated region there must be reconstructed the proper set of climatic and 

 topographical conditions which the phenomena there exhibited may seem to 

 demand. This can only be done after all the fiicts have been thoroughly 

 studied out. It is jjelieved, however, that enough is known already to war- 

 rant the assertion tliat a general refrigeration of the earth could never have 

 caused that peculiar distribution of snow and ice to which the term Glacial 

 epoch is commonly applied ; and that the phenomena in question are en- 

 tirely compatible with a higher mean temperature than now prevails. 



Finally, it will be desirable that we should review the various theories 

 which have been proposed to account for '" glacial climates," and especially 

 those which look to a recurrence of heat aud cold, or at least of conditions 

 favoring the development of ice in abnormal quantity, on the two hemi- 

 spheres alternately. In the course of this discussion it will become evident 

 that the present writer is by no means alone in his view of the couipatibility 

 of a generally higher mean temperature of the earth with a greater extension 

 of ice over certain rotrions. 



