Age of the Pinnacle Series. 17^ 



posited in the sea as strata of sand, mud, etc., they were consoli- 

 dated, overthrust, faulted, and upheaved into one of the grandest 

 mountain ridges on the continent. Then, after the mountains 

 had reached a considerable height, if not their full growth, the 

 snows of winter fell upon them, and glaciers were born ; the 

 glaciers increased to a maximum, and their surfaces reached 

 from a thousand to tAVO thousand feet higher than now on the 

 more southern mountain spurs, and afterward slowly wasted 

 away to their present dimensions. All of this interissting and 

 varied history has been enacted during the life of existing species 

 of plants and animals. 



The relative age of the Yakutat and Pinnacle series is the 

 weakest point in the history sketched above. The facts on which 

 it rests are as follows : At Pinnacle pass the sandstones and 

 shales forming the southern wall belong to the Yakutat system 

 and are much disturbed, while the northern wall, or the heaved 

 side of the fault, is composed of the rocks of the Pinnacle sys- 

 tem, inclined northward at an angle of 30° or 40°. North of 

 this fault-scarp, in the foothills of Mount Owen, sandstones and 

 shales, seemingly identical Avith those of the Yakutat system, 

 again occur, although their direct connection with the rocks 

 south of Pinnacle pass was not observed, owing to the snow that 

 obscured the outcrops. Again at Dome pass a similar relation 

 seems evident, but cannot be directly established. The imme- 

 diate foothills of Mounts Augusta, Malaspina, and St. Elias are 

 also of sandstone, lithologically the same as the Yakutat series. 

 The conclusion that the Yakutat system is younger than the 

 Pinnacle-pass rocks was reached in the field after many other 

 hypotheses had been tried and found Avanting, and to my mind 

 it explains all the observations made. Ea^cu should the sup- 

 posed relations of the two series under discussion be rcA^ersed, it 

 Avould still be true that a A^ery large part of the rocks of the St. 

 Elias region Avere deposited since the appearance of liAdng species 

 of mollusks and plants, and that the prevailing structure of the 

 region Avas imposed at a still later date. This Avill appear more 

 clearly after examining the structure of the region. 



St. Elias Schist. 



The rock forming several thousand feet of the upper portion 

 of the St. Elias range is a schist in which the planes of bedding 



24— Nat. Geor. Mag., vol. Ill, 1n91. 



