TIIK SI'CCHSSIOX OF DKPOSITS. 33 



iiiiuitlc (if ice, tlioiiu'h tlicic iiiiisl ill ceilaiii jHiiods have 

 boLMi vt'i'V cxti'iisivc local iilacicis on the Apitalachiaiis, tlic 

 Laiu'c'iiliaii axis and llic iiioiiiilaiiioiis icj^nniis of the 

 west.* The two latter hasc Ix-cii named liy Dr. (1. M. 

 Dawson lli(! "Luurenlide" and " ( 'ordilleran " ^'laeiers 

 i'es))ectively. The i'oi'iner "lav lie named tin " Aiipala- 

 C'hiaii " glacier, and these three must have been the 

 principal sources of land ice in the height of the glacial 

 age, when large; portions of the plains and valleys must 

 have been suhmeigccl. It does not, indeed, seimi ])ossil»le 

 that, under any conceivalile meteorological eoudilions, an 

 area so e.\ti'nsi\e as that of ('anada, if existing as a land 

 surface, should receive, exci'iit tm its oceani( margins, a 

 sullieient amount of precipitation to produce a continental 

 glacier.f 



in the great ('ordilleran ranges of the noilh-vvest the 

 changes e\idenced in the east occurred in an exaggerated 

 form. The general character and prohal)le com[)lexity 

 of these changes may lie seen from the following provi- 

 sional table taken fidin Dr. ( ». ^l. Daws(jn,and the evidenc(! 

 for which will be found in his memoir on the " I'hysio- 

 grajihical (Jeology of the Kocky Mountain llegion of 

 Canada,"'.! already rt'ft'rred to. 



* a. M. Dawson, Reports on IJritisii Coluiultiii, iiml Superficial 

 (ieology of British Coliunltia, Journal (<eol. Society, KS7S. Memoir 

 on Rocky Mountains, Trans. R. S. C, 1S!M). 



t The term "modified drift," sometimeis used for tiie upper pleis- 

 tocene deposits, is ol)jectioual)le. The gravels and sands of tlie Saxicava 

 sand are no more "modified" representatives of the lower beds tlian a 

 carboniferous sandstone or conglomerate is a modification of underlying 

 strata. Tlie term lias no proper significance, unless it could be siiown 

 that the boulder clay is a deposit formed on land and subse(iuently 

 modified by aijueous action. ~-^. _ , 



I Trans. R. S., Canada, 1890. 



