88 G. M. DAWSON ROCKY MOUNTAIN RKGIOX IX CANADA 



from a geolooical point of view, and the Laramide range, as first pro- 

 duced, may ver}^ possibly have attained a height approaching 20,000 

 feet.* The thickness of stratified rocks in the geosyncline was at the 

 time probably more than 40,000 feet. 



It is difficult to determine to what extent tlie Archean axis with the 

 Gold ranges and other preexisting mountains were affected at tliis period 

 of orogenic movement, because of the absence of the. newer formations 

 there, but it seems probable that no ver}^ important change took place. 

 Fartlier west, however, the great zone of Coast ranges was elevated, and 

 the corrugated and vertical Cretaceous ])eds met with even on their in- 

 land side, show that large parts of the Interior plateau of British Colum- 

 bia and of the country in line with it to the northward were flexed and 

 broken. Similar conditions are found to have affected the Cretaceous 

 rocks of Vancouver and the Queen Cliarlotte islands, of which the moun- 

 tain axis, previously in existence, was evidently greatly increased in 

 elevation. 



The Laramide geosyncline has already been i)articularly referred to 

 and allusion has been made to the now well recognized fact that by 

 such zones of continued subsidence and dei)osition the lines of most 

 mountain systems have been determined. To the Laramide geosyncline 

 here, the mountains of the Archean axis — the (Jold ranges— stood in 

 much the same relation as tlie Archean western border of the Wasatch 

 to the Laramide geosjmcline in Utah (as described by Dana), but on a 

 larger scale. 



On the other or western side of this axis, as already noted, I am now 

 led to regard the zone of country extending to the Vancouver range as 

 a second and wider geosyncline, with a breadth of about 200 miles, in 

 which a thickness of deposits })erhap3 greater than that of the Laramide, 

 but in the main composed of volcanic ejectamenta, had by this time been 

 accumulated. The volume of the Carboniferous and Triassic rocks alone 

 must have exceeded 20,000 feet. It is ])robable that to this may be 

 added a great thickness of older rocks,t ^^^^' the circumstance that vol- 

 canic action was so })ersistent here, and the amount of extravasation 

 resulting from it was so enormous, implies a recognition of the fact that, 

 along this zone (not far from the edge of the continental plateau) the 



*Tliis refers particularly to the better known region near the Bow pass. See Annual Report, 

 Geol. Surv. Can. (N. S.), vol. ii, p. :5l D, and Am. Jour. Sei., vol. xlix, p. 403. The base of the 

 mountains may at this time have been nearly at sealevel, or 4,000 feet lower tlian at present, while 

 the actual heigiit at anj' time attainfnl would depend upon the rapidity of uplift relatively to de- 

 nudation. The total height of folded strata is estimated at from 32,000 to 35,000 feet. 



tSeveral tliousand feet of Cretaceous rocks must also be added to this thickness near the line 

 of the present Coast ranges, and the total thifknoss of deposits in the center of this geosyncline 

 must probably have exceeded 40,0()0 feot. 



