72 G. M. DAWSON — ROCKY MOUNTAIN REGION IN CANADA 



its vicinity, as well as on the Queen Charlotte islands, are rocks very 

 similar in composition to those of the Cache Creek of the interior, but 

 still differing somewhat from these in aspect. They comprise lime- 

 stones and volcanic accumulations preponderantly, with occasional 

 zones of argillite. The limestones are usually in the form of marbles, 

 often coarsely crystalline, but from them a few fossils referred to the 

 Carboniferous period have been obtained. The volcanic materials in- 

 clude amygdaloids, agglomerates, and tuffs, but are often converted to 

 schists, and sometimes become mica-schists or imperfect gneisses, as in 

 the vicinity of Victoria. Their degree of alteration is very different 

 locally, and their aspect consequently varies much from place to place, 

 but on the whole they evidence conditions of deposition much like 

 those of the Cache Creek group.* The^^ have unfortunately not yet 

 been made the subject of any detailed study, and they are again in- 

 volved with Triassic strata closely resembling them in aspect. 



Triassic 



In my report for 1877 f the existence in British Columbia of rocks 

 shown by their fossils to be referable to the Triassic was made known, 

 and these rocks, as developed in the Interior plateau region, were named 

 the Nicola series or formation. This rests, at least in some places, un- 

 conformably upon the Carboniferous, and no rocks representing the 

 Permean period have been identified. The Nicola formation is, how- 

 ever, chiefly composed of volcanic materials, the intercalated limestones 

 or argillites in which fossils are occasionally found being few and far 

 between. The greater part of its mass is undoubtedly Triassic, but the 

 highest beds in a few places have yielded a small fauna that is referred 

 by Professor Hyatt to the Lower Jurassic. All the fossils are marine.| 



Partial sections of the Nicola formation have been obtained in a num- 

 ber of places, but its study is attended with difflculty. owing to the very 

 massive and uniform character of the most of its rocks, the region cov- 

 ered by it being best characterized as one of " greenstones." These rocks 

 often closely resemble those of the Carboniferous, and in some places it 

 is not easy to separate them, on the other hand, from the older Tertiary 

 volcanic materials. Lithologicall}^ the rocks are chiefl}^ altered diabases 

 of green, gra}^ blackish, and purplish colors. In regard to state of ag- 

 gregation, they comprise effusives (often amygdaloidal), agglomerates, 

 and tuffs, the latter showing evidence of subaqueous deposition through- 



*GeoI. Mag., Decade II, vol. viii, p. 219. 

 t Report of Progress, Geol. Surv. Can., 1877-'7S. 



X Fossils of the Triassic rocks of British Columbia, J. F. Whiteaves, Contributions to Canadian 

 Paleontology, vol. i, part 2. Annual Report, Geol. Surv. Can., vol. vii (N. S.), p. 4D B et seq. 



