TKHTIAKY «^1 



junction of the Coldwater and Nicola rivers, bituminous coal. At the 

 l)ase the conglonierates are often rough and coarse, composed of the local 

 underlying rocks, upon which they rest irregularly, hut above these, in 

 several places in the southern part of the Interior plateau, are thick beds 

 of well rolled and generally small pebbles derived for the most i)art from 

 the cherty beds of the Cache Creek formation. The sandstones and 

 shales are usually pale-colored, gray, bufif, or drab, except where they 

 become carbonaceous * 



Speaking of the southern part of British Columbia, where the Tertiary 

 deposits have been examined with some care, it ap[)ears that the beds 

 of the Cold water group were, at least locally, disturbed and subjected to 

 considerable erosion before the deposition of the overlying materials as- 

 signed to the Miocene. These are almost entirely of volcanic origin, 

 and over a considerable area they admit of separation into lower and 

 upper volcanic groups, between which are the water-laid Tranquille beds. 



The i)rincipal volcanic vents of the early Miocene appear to have been 

 situated near to and parallel with the inland border of the Coast ranges, 

 their denuded remnants being now found in the Clear mountains, II- 

 gachuz mountain, etcetera. Both effusive and fragmental rocks are 

 represented in the products of this period, which, petrographicall}'' 

 considered, consist chiefly of augite-porphy rites, of gra}'', greenish, and 

 purplish colors, with smaller amounts of mica-porphyrites, picrite-por- 

 phyrites, etc. These generally form massive beds, and are now found in- 

 clined in many places at angles as high as 30 degrees from the horizontal, 

 although to what extent this may represent the natural slope of deposi- 

 tion and in how far it may be due to subsequent movement is often 

 indeterminate. 



The Tranquille beds consist generally of bedded tuffs, and are usually 

 pale in color. They occasionally contain plant remains and some thin 

 beds of coal or lignite, as at Kamloops.f The upper volcanic group is 

 composed for the most part of basalts and basalt-breccias, with smaller 

 quantities of various porphyrites, mica-trachyte, and mica-andesite. 

 The basalts often occur in horizontal flows of great extent, their eruption 

 having marked the closing stage of the great Tertiary period of vulcanism. 

 Their sources may have been numerous and local, and they are often 



* The Kenai formation of Dall, found in some parts of Alaslca, is believed by Dall to be either 

 Oligoeene or Eocene. The statement, however, that the Kenai is also " widely spread in British 

 Columbia" is too comprehensive. It may be supposed to refer to formations like that here de- 

 scribed, widely separated geographically and ditfering in conditions of deposition from the typi- 

 cal Kenai of Cooks inlet. In such a case the elevation of a local formational name into a re- 

 gional chronological term is in no way helpful and should, I think, be deprecated. (See Bull. 

 No. 84, U. S. Geol. Survey, Annual Report, U. S. Geol. Survey, 1895-96, part i, p. 481. Ibid., 

 189G-'07, part ii, p. .345.) 



t Annual Report, Geol. Surv. Can. (N. S.), vol. vii, p. 169 B. 



XII— Rtir.r,. Groi.. Soc. Am., Vor„ 12, 1900 



