216 WARREN UPHAM^ ESQ., ON CAUSES OF THE ICE AGE. 



dni'iuo' the late Pliocene and early Quaternary periods.* In 

 iK)i-tliern California, Professor George Davidson, of the 

 United States Coast Survey, reports three submarine valleys 

 aboiit twenty-five, twelve, and six miles south of Cape 

 Mendocino, sinking respectively to 2,400, 3,120, and 2,700 

 feet below the sea level, where they cross the 100 fathom 

 line of the marginal plateau.f If the land there were to rise 

 1.000 feet, these valleys would be fjords Avith sides towering 

 high above the water, but still descending beneath it to 

 great depths. 



33 Farther to the north, Puget Sound and the series of sheltered 

 channels and sounds through wdiich the steamboat passage is 

 made to Glacier Bay, x\laska, are submerged valleys of erosion, 

 now filled by the sea bat separated from the open ocean by 

 thousands of islands, the continuation of the Coast Range of 

 mou)itains. From the depths of the channels and fjords Dr. 

 G. j\I. Dawson concludes that this area had a preglacial 

 elevation at least about l>()0 feet above the present sea level, 

 during part or the whole of the Pliocene period. | 



34 Le Conte has correlated the great epeirogenic uplifts of 

 North America, known by these deeply submerged valleys on 

 both the eastern and western coasts, with the latest time of 

 orogenic disturbance by faulting and upheaval of the Sierra 

 Nevada and Coast Range in California, during the closijig 

 stage of the Tertiary and the early part of the Quaternary 

 era, culminating in the Glacial period. § In the Mississippi 

 basm, from the evidence of river cru'i'cnts much stronger than 

 now, transporting Archean pebbles from near the sources of 

 the iMississippi to the shore of the Gulf of Mexico, Prof. E. W. 

 Hilgard thinks that the preglacial uplift, inaugurating the Ice 

 age, was 4,000 or 5,000 feet more in the central part of the 

 continent than at this river's mouth. || 



35 Although the adequacy of the preglacial epeirogenic 

 elevation of this continent to produce its Pleistocene ice-sheet 

 was tardily recognized, it was distinctly claimed by Dana in 

 1870 that the Champlain subsidence of the land beneath its 

 ice load, supposing it to have been previously at a high 



* DaUetin of the California Academy of Scietices, vol. ii, 1887, pp. 

 5 1 .-)-;■) 20. 



+ J hid., vol. ii, pp. 2fi5-268. 



I Canadian iVaturalist, new series, vol. viii, pp. 241-248, April, 1877. 



i^ Bailetin Geol. Son. of America, vol. ii, 1891, pp. 323-330; Elements 

 of Geology, third edition, 1891, pp. 562-569, 589. 

 ' ll Am. Joar. of Science, III, vol. xliii, pp. 389-402, May, 1892. 



