7(1 'IIIK ICH .\(;k i\ caxada. 



ciitiU'lyiiiic oscilliitions of Icxcl mul :i iiiirlial siilisidciuco, 

 which is ;i|)](ar('iilly still in innnrt'ss.* 



I'd!' llic evidence lit' this hislnry 1 may refer tn the 

 l^apei's eileil in the iKites.f where ahundant facts will he 

 found I'elatin;^' inoi'e especially tn ( 'anada, and, so far as 

 my readiu},' extcMids, ihey will he hmnd applicahle, with 

 certain modifications of details, to oihei' parts of the 

 nortiiern hemisphere. 



In closiiiu; this section, 1 desire to refer to the nia]> 

 (Ki^-. (i, r>.) of the <fi'o<i'ra]ihy of Xorlh America in the 

 early rieistoceiie, the hciuhl of tla; «;lacial pi-riod. At 

 this time. I l)tdie\e the northern half of North .Vmericu 

 consisted of thri'e larj^e and monntainons islands, clad for 

 the most part with neve and ^'laciers, and surrounded l)y 

 iee-laden sens and straits. The conditions, it will l>e seen 

 at a ^dance, wer(! most favourahle to refri^'eration, hy 

 accumulation of floating \vv in temperate latitudes, while 

 the arctic climate may have been littli! more severe than 

 at ])resent, and the extreme o[)iMtsiie of those which 

 existed in the warm i)eriod of the early tertiary, when 

 the northern end of the continent was closed a«i:ainst the 

 arctic currents, and when the interior continental plateau 

 constituted a northern extension of the warm waters of 

 the gidf of Mexico. This map inii)lies dillerential de- 

 pression of the western plains as compared with the 

 mountains, and of the northern as compared with the 

 southern portions of North America, and an opening for 



* Accurding to Merrill and Lendenkehl (American Journal Science, 

 June, 1891), alternate depression to the amount of loO feet and eleva- 

 tion to the amount of 400 feet have occurred in the valley of the 

 Hudson river since the glacial period. See also Acadian (Jeology, 

 article "Submarine Forests." 



+ Also notes on Canadian Pleistocene, 1872; Acadian Geology, 1878. 



