164 



tain torsos must have been the rule, except on the lava 

 plains. In short, the early Pliocene Cordillera was a torso 

 landscape, locally veneered with, and smoothed by, basaltic 

 floods. It was this topographic composite, already close 

 to sea level, which early Pliocene erosion somewhat further 

 reduced toward a base level of fairly constant position. 



Toward the close of the Pliocene all or nearly all of the 

 Canadian Cordillera seems to have been elevated, to heights 

 varying considerably, but reaching maxima of from 2,000 

 to 4,000 feet (610 to 1,220 m.). The streams so rejuven- 

 ated have had time to sink deep valleys in all three of the 

 great Cordilleran Belts. This two-cycle topography is 

 specially well illustrated in the Belt of Interior Plateaus, 

 but it can be discerned in the Rocky Mountain trench, in the 

 region around Revelstoke, and elsewhere along the railway 

 section. The plateaus of the interior have been thus iso- 

 lated from one another. In part, they represent dissected 

 lava tables; in part, dissected local peneplains of pre- 

 Miocene date; in part, dissected mountain torsos, reduced 

 during the early Tertiary and the Mesozoic. There is no 

 evidence that a general peneplain was developed over this 

 part of the Cordillera at any time ; nor is it proved that the 

 upland facets of the Interior Plateaus were due to general 

 peneplanation of that broad belt in late Miocene and early 

 Pliocene time. A superficial study of the Interior Plateaus 

 might lead to that conclusion; in reality, the upland relief 

 has been conditioned by several pre-Miocene erosion 

 cycles. 



The Pleistocene glaciers gradually overwhelmed a mature 

 to sub-mature topography. Their work represents a 

 chapter of Cordilleran history already sketched; some of 

 its details will be noted in annotations on the route to be 

 followed by the excursionists. The recent changes in the 

 late Glacial landscape are relatively slight and for the 

 most part are too obvious to need formal statement in 

 this place. 



SPECIALLY NOTEWORTHY FEATURES. 



In the midst of a multitude of problems and ascertained 

 facts, certain aspects of the Cordilleran geology are worthy 

 of special attention. Some of these are here listed for the 

 convenience of the excursionists. 



