Warren Upham — Pleistocene Climatic Changes. 347 



Atlantic side of the eastern continent has been greatly uplifted, 

 attaining as high an altitude as that which Sir A. C. Eamsay and 

 James Geikie conjectured as a possible cause of the frost-riven 

 limestone-agglomerates of Gibraltar.^ 



Wherever great movements of land elevation have taken place 

 in high latitudes, either north or south, which received abundant 

 precipitation of moisture, ice-sheets were formed ; and the weight 

 of these ice-sheets, as was first pointed out by Jamieson, seems to 

 have been a chief cause, and often probably the only cause, of the 

 subsidence of these lands and the disappearance of their ice. 

 Though the still high surface of the greater part of an ice-sheet 

 would not be affected by the temperate climate of the country 

 depressed to its present level or slightly lower, the warm summers 

 along the ice-border would cause it to be rapidly melted, and 

 by the extension of this process inward all the ice-sheet would 

 disappear. When the progress of the marginal melting in the 

 Mississippi basin had given generally steep gradients to the ice- 

 front, its more powerful currents formed the retreatal moraines and 

 the many lake iDasins of the unevenly laid later drift which are so 

 strongly contrasted with the smooth and attenuated outer portion of 

 the drift-sheet beyond the moraines. 



What were the original sources of the energy displayed in the 

 earth-movements of uplift preceding glaciation, and why this has 

 been so extensively developed during the Quaternary era, are very 

 difficult questions which it is not the purpose of this paper to 

 consider, since I have attempted elsewhere to answer them, in 

 an appendix of Wright's "Ice- Age in North America." It may 

 be properly noted, however, that the explanations mentioned are 

 entirely consistent with Dana's teaching that the great continental 

 and oceanic areas have been mainly permanent from very early 

 geologic times. 



The chief objection urged against this explanation of the causes 

 of the Glacial period and its sudden end consists in an approximate 

 identity of level with that of to-day having been held by some 

 drift-bearing areas at a time very shortly preceding their glaciation. 

 This is clearly known to have been true of portions of Great 

 Britain and of New England. In respect to this objection, it must 

 be acknowledged that the pre- Glacial high elevation which these 

 areas experienced was geologically very short. With the steep 

 gradients of the Hudson, of the streams which formed the now- 

 submerged channels on the Californian coast, and of the Congo, 

 these rivers, if allowed a long time for erosion, must have formed 

 even longer and broader valle3's than the yet very impressive 

 troughs, continuing to depths of 2000 to 6000 feet beneath the sea- 

 level, which are now found on these submarine continental slopes. 

 But the duration of the epeirogenic uplift of these areas on the 

 border of the glaciation for the Hudson, beyond it for the Californian 

 rivers, and near the Equator in Western Africa, can scarcely be 

 compared in its brevity with the prolonged high altitude held 

 ^ Quart. Journ. Geol. Soc. vol. xxxiv. 1878, pp. 505-541. 



