doubtedly been from oilier points of view. The valleys of the liord-like 

 lakes that oeeur alonir the Hanks of the Arehean axis of the interior may 

 })rohal)ly also be referred to liver erosion in the later Pliocene, bnt if so 

 this mountain region must have been affected by a relatively greater 

 uplift at that time, followed later by a subsidence of its central part. It 

 appears, however, that the excavation of valleys or gorges like these by 

 rivers, when the slope and water supply are favorable, occurs with such 

 rapidity relatively to the wider effects of denudation, as to be almost 

 negligible in an}' general view of the physical changes of an extensive 

 region or in the accounting of geological time. 



There is as yet some ditiiculty in connecting the later physical changes 

 t)articularly referred to above with those which have recently come 

 under observation far to the north in the Klondike region. It is prob- 

 able, however, that the auriferous "quartz drift" of that region, imply- 

 ing long subaerial deca}' and stability of level, may be attributed to the 

 early Pliocene; while the river gravels found in the newer and deeper- 

 cut valleys may be assigned to the later Pliocene time of greater eleva- 

 tion. During the Pliocene, and ])robabl_y until its close, the mammoth, 

 one or two species of bison, the moose, and other large mammals roamed 

 northward to the Arctic sea. Then came the Glacial period, with re- 

 newed great changes in levels and climate and its own peculiar records 

 and history, which in man}' respects are more difficult of interpretation 

 than those of more remote periods, because the whole time occupied 

 by them has been relatively so brief I have elsewhere endeavored to 

 follow this history in detail, and do not propose on this occasion to 

 deal with this latest chapter of the physical history of the Rocky Moun- 

 tain region of Canada. 



In conclusion, what appear to be the most striking points evidenced 

 by the geological record of this northern part of the Cordillera perhaps 

 be specified as follows : 



(1) The great thickness of strata accumulated both to the east and 

 west of an Arehean axis. In the Laramide geosyncline the strata no 

 doubt actually attained the volume stated. In the western and wider 

 syncline it is not so certain that all the formations in their full thickness 

 were ever actually superposed at any one place or time (for reasons 

 already alluded to), but the volume was probably not less than in the 

 Laramide region. 



(2) The great proportion of volcanic materials accumulated in the 

 western geosyncline and the recurrence of vulcanism throughout the 

 geological time-scale in this region, resulting in the production of massive 

 ^volcanic formations in the Cambrian, Carboniferous, Triassic, Creta- 

 ceous, and Miocene. 



