214 WARREN UPHAMj ESQ., ON CAUSES OF THE ICE AGE, 



pve,Li,'lacial elevation which could be thus affirmed was 

 evidt'utly too little to be an adequate cause for the 

 cohl and suowy climate producing the ice-sheet. The 

 belief that this upHft was 8 000 feet or more, giving" 

 sufficiently cool climate, as Professor T. G. Bonney has 

 showni, to cause the ice accumulation, has been only reached 

 Avithin the past few years through the discovery by sound- 

 ings of the U,S. Coast Survey, that on Ix^th the Atlantic 

 and Pacific coasts of the United States submarine valleys 

 evidently eroded in late Tertiary and Quaternary time reach 

 to profound depths, 2,000 to 3,000 feet below the present sea 

 level, 



26 Pi'ofessor J. W. Spencer has very impressively reviewetl 

 the evidences of the formerly higher altitude of the North 

 American continent, immediately before the Ice age.* 

 'i'hough he has not proceeded to interpret these observa- 

 tions as revealing in continental elevation the probable cause 

 of the colder climate and accumulation of ice-sheets during 

 the Glacial period, I believe that this is a legitimate con- 

 clusion, and that it strongly reinforces the arguments long 

 ago advanced by Lyell and Dana and recently emphasized 

 anew by Wallace. The submarine border of the continental 

 plateau of North America to depths of more than 3,000 feet 

 is cut by valleys or channels, which if raised above the sea 

 level would be fjords or canons. These can be no other 

 than river-courses eroded while the land stood much higher 

 than now ; and its subsidence evidently took place in a late 

 geologic epoch, else the channels would have become filled 

 Avith sediments. 



27 According to the Coast Survey charts, as noted by Spencer, 

 the bottom of a submerged valley just outside the delta of 

 the Mississippi is found by soundings at the depth of 3,000 

 feet. This valley is a few miles wide and is bounded by a 

 plain of the sea bed from 900 to 1,20;) feet above its floor. 

 It thus appears that the country north of the Gulf of Mexico 

 has been raised for a short time to a height of not less than 

 3,000 feet. 



28 The continuation of the Hudson river valley has been 

 traced L y detailed hydro graphic surveys to the edge of the 



* Bulletin oj the Geological Sodtty of America, vol. i, 1890, pp. 65-70, 

 with map of the pieghicml i^aurentian river ; vol. v, 1893-94, pp. 19-22, 

 -with map of subiuaiiue contour in the West Indies region. The first of 

 tliese papers was also in the Geol. Magazine, III, vol. vii, 1890, pp. 208-212. 



