538 



INDEX TO THE STKATIGRAPHY OF NORTH AMERICA. 



granitic rocks. They have not, however, been deposited upon a granitic floor, as the granites 

 are evidently later in date than the rocks of the Vancouver series, and nothing whatever is 

 known of the character of the surface upon which its volcanic and other associated beds were 

 originally formed. 



The fossils obtained from the Vancouver Triassic are described by Whit- 



eaves. 



M 10. KAMIiOOPS DISTBICT, SOUTHERN BRITISH COLUMBIA. 



The Nicola formation, which consists largely of volcanic rocks with associated 

 fossiliferous marine sediments, was originally assigned by Dawson in 1878 to the 

 Triassic on somewhat meager evidence. In 1894 Dawson ^"* reviewed all the 

 evidence which had then accumulated and concluded : 



It will be observed that the original reference of the series as a whole to the Triassic has 

 been gradually strengthened by later discoveries. These, taken in connection with. the 

 stratigraphy, in fact seem to show that while the great bulk of the Nicola formation is undoubt- 

 edly equivalent to the Triassic, it passes up in a few places into rocks of Lower Jurassic date. 

 The structure and lithology do not appear to afford any means of separating the two faunas 

 or of drawing any line through the great mass of rocks, chiefly of volcanic origin, in which 

 they occur, and it is therefore appropriate and necessary to treat of the Nicola formation as a 

 whole, although recognizing the fact that it probably extends higher than the typical Trias. 



An unconformity is indicated between the lowest strata of the Nicola and the 

 underlying Paleozoic rocks. Regarding the composition of the Nicola formation 

 Dawson says : 



Within the area of the Kanoloops sheet the Nicola formation consists essentially of a great 

 mass of volcanic deposits, with a total thickness of probably 10,000 to 15,000 feet. In the 

 lower part of the formation some thin and probably irregular beds of hmestone occur. Here 

 and there throughout the formation a limited thickness of argiUites is found, and, forming 

 the summit, so far as yet ascertained, is another bed of hmestone. 



The greater part of the volcanic rocks may be described geaeraUy under the useful name 

 of "greenstones." LithologicaUy, these rocks are for the most part found to be altered dia- 

 bases, with, exceptionally, augite porphyrites, also considerably altered. In regard to their 

 state of aggregation, these volcanic materials represent all the usual products .of eruptions, 

 including effusive rocks, sometimes amygdaloidal, and tuffs. There is also, throughout the 

 entire series, more or less evidence of subaqueous deposition and bedding, whUe no proof has 

 so far been obtained in this district of the existence of subaerial accumulations. 



The following summarized general sections, based on more detailed descriptions given 

 in. the sequel, best represent what is known of the Nicola formation, in the eastern and western 

 parts of its area respectively. The sections are in descending order. 



Thompson River, south, of the Ashcroft Cretaceous area. 



Feet. 



Limestone (20 feet or more) 20 



Fine-grained feldspathic rocks, sometimes well 

 bedded, generally gray 1, 800 



Tuffs, or ash rocks, passing into agglomerates, 

 with some fine-grained felsitea, gray, purplish 

 and green; a few small limestone beds near the 

 base 7, 840 



Chiefly green diabase agglomerates, often coarse. 

 Several calcareous beds and limestones. Dark 

 felsites at base 3, 930 



Approximate total 13,590 



Vicinity of Nicola Lake. 



Feet. 



Fine-grained feldspathic rocks, generally well 

 bedded 1, 200 



Diabases, chiefly effusive and sometimes amygda- 

 loidal; some tuffs; two thin beds of limestone 

 near the base 3, 700 



Chiefly green diabase agglomerates, occasionally 

 amygdaloidal. Thickness at least 2,600 feet and 

 possibly 6,000 feet (say) 2, 600 



Approximate total (minimum) 7, 509 



