138 C. W. Hayes — Expedition through the Yukon District. 



in a position to control the movements of his party, and so was 

 able to give more than a passing glance to points of special im- 

 portance. Since the writer was without previous acquaintance 

 with the rocks of the Cordilleran system and had no opportunity 

 for observation, except as it was afforded along the route or at 

 stops selected without reference to the geology, the information 

 obtained is offered only as supplementary to the observations 

 made by others and as preliminary to the more thorough study 

 of those who may hereafter visit the region. 



Rocks of Taku Valley.— T\ie section afforded by Taku river as it 

 cuts through the Coast range is quite similar to those described 

 by Dawson on Stikine river and Chilkoot pass. After leaving 

 the argillites of the coast, which extend to near the head of Taku 

 irdet, a broad belt of gray hornblende granite is crossed ] this is 

 called the Coast Range granite by Dawson. The belt is about 

 forty miles in width, extending nearly to the South fork of 

 the Taku. In addition to the granites, this belt also contains 

 altered eruptive rocks in horizontal or undulating and some- 

 times highly contorted beds. 



Rocks of the interior Plateau.— Forming the high plateau between 

 the Coast range and Ahklen valley is a somewhat broader belt, 

 containing a great variety of rocks, both eruptive and sediment- 

 ary but all highly altered. The sedimentary rocks consist of 

 limestones and marbles, shales and slates with conglomerates, 

 sandstones and quartzites. The least altered members of this 

 series are along the western side of the belt. At the junction 

 of the North and South forks of the Taku, near the eastern 

 limit of the Coast Range granites, there are black slaty shales and, 

 apparently overlying them with a clip of from 25° to 50° north- 

 eastward, are compact bluish limestones. Still farther eastward 

 there are siliceous shales with large conglomeratic pebbles of the 

 underlying limestone. The pebbles contain some obscure fossils, 

 probably Carboniferous, which would indicate a Mesozoic or later, 

 age for the shales. These slightly altered rocks occupy a belt 

 about eight miles wide, east of which lies a region traversed by 

 many dikes that have converted probably similar shales and 

 limestones into talcose slate and highly crystalline marble. 



Among the non-sedimentary rocks of this plateau belt there 

 are many basic eruptives largely altered to serpentine, and also 

 considerable areas of granite. A portion at least of the granite 

 is older than the sediments as indicated by basal conglomerates 



