WARREN UPHAM, ESQ., ON CAUSES OF THE ICE AGE. 219 



that a similar valley exists iu the southern parL of the Bay of 

 Biscay. These observations sliow that within very late 

 geologic time, probably almost the entire Atlantic side of the 

 eastern continent, has been greatly uplifted, attaining as high 

 an altitude as that which A. C. Ramsay and James Geikie 

 conjectured as a possible cause of the frost-riven limestone- 

 agglomerates of Gibraltar.* 



38 Likewise the tropical portions of the western continent, tbe 

 West Indies, and the smaller islands of the Caribbean region, 

 appear to have shared the epeirogenic disturbances which 

 were associated with the glaciation of the northern and 

 southern parts of this continent, as is well brought out by the 

 reoent studies and discussions of the geology of Barbados 

 island by A. J. Jukes-Browne and J. B. Harrison,t and by 

 the close relationship of the Pacific and West Indian deep sea 

 faunas on the opposite sides of the Isthmus of Panama, made 

 known through dredging by Alexander Agassiz.l This 

 testimony, indeed, with that of Darwin, L, and A. Agassiz, 

 and others, of very recent, extensive, and deep subsidence of 

 the western coast of tSouth America, apparently however 

 continuing for no long time, lends much probability to the 

 supposition that the low Panama Isthmus was someAvhat 

 deeply submerged for a geologically short period contempor- 

 aneous with epeirogenic uj,)lifts of the circumpolar parts of 

 this continent both at the north and south, whereby the effects 

 of great altitude in covering the northern and southern high 

 areas with ice-sheets were augmented by the passage of much 

 of the Gulf Stream into the Pacific Ocean. 

 3y The end of the Tertiary era and the subsequent Glacial 

 period have been exceptionally characterized by many great 

 oscillations of continental and insular land areas. Where 

 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 seems to have been a chief cause, 

 and often probabl}^ the only cause, of the subsidence of these 

 lands and the disappearance of their ice. 



40 In an appendix of Wright's Ice Age in North America, I 

 have shown that, between epochs of widely extended 



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

 t Quart. Joivni. Geol. Soc, vol. xlvii, 1891, pp. 197-250. 

 I Bulletin, 3fus. Comp. ZooL, at Harvard College, vol. xxi, pp. 185-200, 

 June, 1891. 



