220 WAEREN UPHAM, ESQ., ON CAUSES OF THE ICE AGE. 



mouDtain-building by plication, the diminution of the eartli's 

 mass produces epeirogenic distortion of the crust, by the 

 elevation of certain large areas and the depression of others, 

 with resulting inequahties of pressure upon different portions 

 of the interior, and that these effects have been greatest 

 immediately before relief has been given by the formation of 

 folded mountain ranges. There have been two epochs pre- 

 eminently distinguished by extensive mountain-plication, one 

 occurring at the close of the Paleozoic era, and another 

 progressing through the Tertiary and culminating in the 

 Quaternary era, introducing the Ice age. During the last, 

 besides plication of the Coast range, of the Alps, and the 

 Himalayas, a very extraordinary development of tilted moun- 

 tain ranges, and outpouring of lavas on an almost unprece- 

 dented scale, have taken place in the Great Basin and the 

 region crossed by the Snake and Columbia rivers. With the 

 culminations of both of these great epochs of mountain- 

 building, so widely separated by the Mesozoic and Tertia-y 

 eras, glaciation has been remarkably associated, and indeed 

 the ice accumulation appears to have been caused by the 

 epeirogenic and erogenic uplifts of continental plateaus and 

 mountain ranges. Since the disturbances, with glaciation, 

 closing Paleozoic time, the same combination of events has 

 not recurred until the Quaternary era, which is not only 

 exceptional in its accumulation of ice-sheets, but also in its 

 numerous and widely extended movements of elevation and 

 subsidence, and its mountain-building and renewed upheavals 

 of formerly base-levelled mountain belts. The earth's sur- 

 face is probably now made more varied, beautiful, and grand, 

 by the existence of many lofty mountain ranges, than has 

 been its average condition during the past long eras. This 

 explanation appears to me entirely consistent with Dana's 

 teaching that the great continental and oceanic areas have 

 been mainly permanent from very early geologic times. We 

 may also, I think, be encouraged to the hope and belief that 

 a long time will probably pass before the recurrence of epeiro- 

 genic conditions producing extensive glaciation. As the 

 rainbow is a promise of recurring fruitful seasons, we see no 

 reason for expecting the return of an Ice age desolating the 

 present most populous and prosperous parts of the world. It 

 may be as far hence to its return, if it shall ever come again, 

 as the ten or fifteen million years since the Coal period and 

 tlie Permian Ice age. 

 41 Two formidable objections to this view that the accumu- 



