55 



As mentioned above, the rocks composing the Coast 

 range are dominantly granitic in character, and although 

 mainly granodiorites, they range from gabbros to granites. 

 They were intruded at different times, commencing early 

 in the Jurassic and extending probably up into the Cre- 

 taceous. The geological terranes of the Yukon plateau 

 in Southern Yukon, range in age from apparently Pre- 

 Cambrian to Recent, and include sedimentary, igneous 

 and metamorphic members. 



The succession of geologic events in that portion of 

 Yukon plateau included in Southern Yukon and Northern 

 British Columbia, and particularly that portion traversed 

 in journeying from Skagway to Dawson, will now be pre- 

 sented in so far as they are known. The information 

 available, however, is rather fragmentary, and for long 

 periods the records have been almost or entirely destroyed. 

 Still it is hoped that a brief treatment of the data obtainable 

 will give a general idea, at least, of the various vicissitudes 

 which the district has undergone. 



The oldest records are contained in a group of rocks, 

 partly igneous and partly sedimentary, which consist 

 dominantly of schists, gneisses, and some impure lime- 

 stones. These rocks are extensively developed in the 

 vicinity of Dawson and elsewhere in Yukon, and have 

 given rise to the famous placer gold deposits of the Klondike 

 and other districts. These rocks have been generally con- 

 sidered to be of early Paleozoic age, but recent investigations 

 by the writer [20, 21] tend to show that they are in part 

 or entirely Pre-Cambrian in age. These rocks show that 

 there were accumulated at an early stage in the history of 

 the district, thousands of feet of arenaceous and argil- 

 laceous matter, followed also by great thicknesses of 

 calcareous material, and that vulcanism was active during 

 and after sedimentation. The relative ages of the various 

 members are imperfectly revealed, since all are now greatly 

 metamorphosed, plicated, distorted, and eroded and appear 

 as a group of rocks consisting dominantly of sericite-schists, 

 chlorite-schists, actinolite-schists, quartz-schists, mica- 

 schists, schistose amphibolites, mashed and sheared 

 diabases, greenstone-schists, quartzites, gneisses, and 

 impure limestones. 



Parts of Yukon Territory appear to have been inundated 

 by the sea from early Cambrian to late Carboniferous 

 time, during which time, calcareous sedimentation was 

 apparently continuous. From Dawson southward, how- 



