rn Ysi()(;KArni(Ai, keatukks 61 



to the westward. Tliese ranges are chiefly composed of granitic rocks, 

 which may in the main be regarded as forming a gigantic " bathylite" 

 with minor included masses of sedimentary rocks. It is hiter in date of 

 origin than tlie Triassic period and })robahly experienced a second and 

 much greater elevation at or about the close of the Cretaceous, but is 

 neither so lofty nor so ragged as the Laramide range. The remarkable 

 fiords of the Pacific coast, both those of British Columbia and those of 

 the southern })art of Alaska, are the submerged valleys of this coastal 

 system of mountains, their erosion being probably referable to early 

 Eocene and late Pliocene times, during which the land stood at rela- 

 tively high levels. 



To the west of the Laramide range, and separated from it by a remark- 

 ably long and direct structural valley, is a somewhat irregular and some- 

 times interrupted series of mountain systems to which the general name 

 of the Gold ranges has been applied, and this is referred to further on as 

 the Archean axis of this part of the Cordillera. It embraces the Purcell, 

 Selkirk, Columbia and Cariboo mountains, all including very ancient 

 rocks and evidently representing the oldest known axis of elevation in 

 the province, although it has not remained unaffected by movements of 

 much later date. Peaks surpassing 10,000 feet in elevation still occur 

 in these mountains. 



Between the Gold and Coast ranges, with a width of about 100 miles, 

 is the Interior plateau of British Columbia, a peneplain referred in its 

 main features to the early Tertiary, which has subsequently been greatly 

 modified by volcanic accumulations of the Miocene, and has been dis- 

 sected by river erosion at a still later period. This plateau country is 

 well defined for a length of about 500 miles, declining northward from a 

 height of over 4,000 feet near the 49th parallel to one of less than 3,000 

 feet, and with an average altitude of about 3,500 feet. It is then inter- 

 rupted for some four degrees of latitude by a mountainous country chiefly 

 composed of disturbed Cretaceous rocks, beyond which the surface again 

 declines to the plateau lands of the upper Yukon basin, with its separated 

 mountain ranges. The Interior plateau is throughout very complex in 

 its geological structure, but except where covered by Tertiary accumu- 

 lations it is found to be chiefly underlain by Paleozoic and Mesozoic 

 rocks. 



One more mountain system remains to be noted. This stands upon 

 the real border of the Continental plateau, and is represented by the 

 long ridge-like highlands of Vancouver island and the Queen Charlotte 

 islands. It is evidently broken between these islands, and is not 

 clearly continued in the archipelago of southern Alaska, which seems to 

 be more closel}' connected with tlie Coast ranges of the mainland. The 



