G. M. Dawson — Geology of British Columbia. 225 



matei'ial affected the composition of the argillites and other rocks, in 

 progress of deposition, even at a great distance from any of the vents, 

 and the series acquired a great thickness. 



Evidence of some disturbance at the close of the Carboniferous 

 period is found in the unconformable superposition of the Nicola 

 Triassic on these rocks, in the southern portion of the interior of the 

 Province. This, however, appears to have affected the region to the 

 west of the land barrier alone, and to have resulted in the more com- 

 plete definition of this barrier, and probably to its increased elevation : 

 for in Triassic and Jurassic times we find the deposition of the red 

 beds and flaggy dolomitic limestones with salt, going on to the east 

 near the 49th parallel, and further south the actual inclusion of salt 

 and beds of gypsum, proving that this region was then a shallow 

 inland sea cut off from communication with the ocean. To the west 

 of the land barrier on the contrary, in the Triassic, and probably 

 also in the Jurassic, a great thickness of volcanic rocks with lime- 

 stones and argillites was being formed along the border of the 

 Pacific. The argillites of this period probably afterwards became 

 the chief gold-bearing formation of tlie country, as is proved to have 

 been the case in California. These with the volcanic accumulations 

 doubtless represent the Star Peak and Koipato groups of the Triassic 

 as described by King on the 40th parallel between the Sierra Nevada 

 and the Wahsatch Kanges ; and though, as elsewhere stated,' I have 

 not been able to find that the existence of Carboniferous volcanic 

 rocks has been recognized in the Sierra Nevada of California, it seems 

 probable, from the description and appearance of the rocks, that more 

 or less altered volcanic materials, perhaps both of Mesozoic and 

 Palaeozoic age, enter into its composition. A further circumstance of 

 interest in connexion with the Jura-Trias period is the evidence now 

 obtained that the sea ajDparently spread uninterrupted!}'- eastward 

 across the Kocky Mountains and into the Peace Eiver country, at 

 least as far south as the 55th parallel. This is proved both by the 

 lithological character of the rocks, and the fossils they contain,^ and 

 ■we thus arrive at an approximate definition, not only of the western 

 but also of the northern limits of the great inland sea, which extended 

 south-eastward to New Mexico, though we still remain ignorant of 

 the precise character of the northern barrier. This period was closed 

 by a great disturbance along the whole Cordillera region. In 

 California the Sierra Nevada rose up as a mass of crumpled and 

 compressed folds. In the southern part of British Columbia the 

 disturbance affected the region from the Gold Range to the coast, 

 extending the land area westward to the 121st meridian, and giving, 

 so far as is known, the first upthrust to the mountains of Yancouver 

 and Queen Charlotte Islands, but forming no continuous range where 

 the great belt of coast mountains now is. 



In the earliest beds of the Cretaceous there is evidence of a general 

 slight subsidence in progress, with the formation of conglomerates, 

 and we can trace the shore-line of the Cretaceous Pacific, which 



1 Geol. Mag. 1877, p. 315. 



2 See, on the latter point, Report of Progress, Geol. Survey, 1876-7, p. 158. 



DECADE II. — VOL. VIII. NO. V. 15 



