CARBONIFEROUS 71 



canic material witli serpentine and interstratilied liniestoneH. The 

 volcanic materials are most al)undant in tlie ui)per part of tliis division, 

 largely constituting it. The minimum volume of the strata of tliis 

 division is about 6,500 feet. The upper division, or Marble Canyon 

 limestones, consists almost entirely of massive limestones, but with 

 occasional intercalations of rocks similar to those characterizing the 

 lower part. Its volume is about 3,000 feet. 



Tlie total thickness of the group in this region would therefore be 

 about 9,500 feet, and this is regarded as a minimum. The argillites are 

 generally dark, often black, and the so-called cherty quartzites are prob- 

 ably often silicified argillites. The volcanic members are usuall}^ much 

 decomposed diabases or diabase-porphyrites, both effusive and frag- 

 mental, and have frequently been rendered more or less schistose b}^ 

 pressure. The serpentine beds are associated with these volcanic rocks, 

 and have evidently resulted from the alteration of some of them. The 

 limestones of both lower and upper divisions hold Fusulina and a few 

 other distinctive Carboniferous fossils, but in the Marble Can3^on lime- 

 stone the most characteristic form is the large foraminifer known as 

 Loftusia Columbiana, entire beds being made up of its debris.f 



Fusuline limestones have now been found in a number of ])laces in 

 the central zone of the Cordillera throughout the length of British Co- 

 lumbia and beyond the 60th parallel, its northern boundar}^ Where 

 these occur the clastic and volcanic rocks associated with them may be 

 definitely referred to the Cache Creek group, but in consequence of 

 the great resemblance of its volcanic rocks to those of the Triassic 

 (as mentioned later), it is often impossible, without close study, to 

 define the area occupied by this group, and its separate mapping has 

 onl}^ as yet been attempted in detail over comparatively small areas. J 



In the southern part of British Columbia, the Cache Creek group 

 shows some evidences of littoral conditions toward the west slopes of 

 the Gold ranges, probably indicating the existence of land areas there. 

 In this vicinity also the Campbell Creek beds, a somewhat peculiar 

 development of argillites, graywackes, and amphibolites, occur. § 



The granitic Coast ranges of British Columbia are much later in date 

 of origin than the Carboniferous, but some of the highly altered beds 

 now included in them or found along their margins are undoubtedly of 

 that period. To the Avest of these ranges, on Vancouver island and in 



* Ibid., p. 46 B. 



t Quart. Jour. Geol. Soc, vol. xxxv, p. G9. 



J Areas included in the Kamloops and Shuswap map-sheets, covering together 12,800 square 

 miles. 

 § Annual Report, Geol. S\irv. Can., vol. vii (N. S.), p. 44 B. 



