REVIEW OF GEOLOGIC INVESTIGATIONS 261 



Circle, partly because it has been worked up in greater detail and partly 

 because both authors are personally familiar with it. The second part of 

 this paper, by Mr Kindle, presents the details regarding the geology of the 

 Porcupine valley, the general results of which will be used in this discus- 

 sion. The senior author has paid more special attention to data here pre- 

 sented bearing on the metamorphic and igneous rocks, while the paleon- 

 tologie studies are entirely the work of the junior author, except where 

 otherwise credited. Mr V. H. Barnett rendered valuable aid throughout 

 the investigation. 



Geology 

 introdvgtioj^ 



The bedrock of the central Plateau region, of which the Upper Yukon 

 l)asin forms a part, includes a broad belt of intricately folded metamorphic 

 rocks, chiefly altered sediments, but with considerable gneisses, schists, 

 and gneissoid and massive granites and some smaller areas of Paleozoic, 

 Mesozoic, and Tertiary terrains, all striking in a general way parallel 

 to the mountain systems and to the southern coastline. This central 

 province is boimded on both sides by high ranges, whose present altitude 

 is due to recent uplift, but whose axes mark loci of crustal movements at 

 least as old as the Lower Paleozoic. To the south are the ranges of the 

 Pacific Mountain system, which are built up in a large measure of Meso- 

 zoic terrains with some Paleozoic rocks, together with large masses of in- 

 trusives. The Eocky Mountain system north of the Yukon is made up 

 chiefly of Paleozoic sediments, with some Mesozoic beds, but with a 

 marked absence of intrusives. 



The Upper Yukon basin includes terrains varying in age from pre- 

 Ordovician to Eecent. While thi-s paper is concerned more especially with 

 the Paleozoic rocks, both the younger and old terrains of the province will 

 be briefly described. The following table presents a concise summary of 

 what is known of the stratigraphic succession : 



