LOWER CRETACEOUS. 627 



In proceeding eastward from the forks to the northern end of Babme Lake, across the 

 intervening mountain region, similar rocks continue to prevail. Sandstones are most abun- 

 dantly represented but contain in some places carbonaceous shales and toward the summit of 

 the pass become associated with rocks of volcanic origin like those before described. These 

 occasionally seem to form fully one-half the thickness of the beds represented. In one place 

 5 nules up the Suskwa River a few impressions of leaves were found. Some of these appear 

 to be coniferous. There is one narrow angiospermous leaf and several grasshke blades. Not 

 far from the summit numerous fragments of sUicified wood were obtained, with a few specimens 

 of a moUusk which, according to Mr. Whiteaves, who has examined the specimens, is a Thracia 

 of the section Corimya. The species is probably undescribed, but it is identical with one from 

 the coal-bearing rocks of the Queen Charlotte Islands. 



In 1875 Dawson ^" distinguished in southwestern British Columbia a great 

 body of volcanic rocks and pyroclastic tuffs under the name "Porphyrite group." 

 He says: 



Porphyrite group. — This name may be provisionally employed to designate a series of rocks, 

 chiefly feldspathic and often porphyritic, though also including diorites of varied texture, the 

 reference of which to any of the groups formerly defined seems uncertain. They are best 

 seen about Tatlayoco Lake, where they overlie unconformably the Cascade crystalline rocks 

 and appear to underlie the beds of the Jackass Mountain series. The whole of the rocks of 

 this group seem to be of igneous origin, though some of them may owe the arrangement of 

 their material to water. 



After the field work of 1876 Dawson ^^ wrote : 



It may now, however, be affirmed with considerable certainty that the rocks called the 

 Porphyrite series in last year's report underlie, probably conformably, the fossiliferous series of 

 Tatlayoco Lake and consequently bear the same relation to the Jackass Mountain beds of the 

 preliminary classification. This inference is chiefly based on the fossils discovered on the 

 Iltasyouco River, described by Mr. Whiteaves in an appended note. 



The most interesting and typical sections of these rocks examined last summer are those 

 in the vicinity of Iltasyouco and Islaho or Salmon rivers. The rocks here seen represent those 

 described last year on Tatlayoco Lake, and though they have not been again observed in contact 

 with the upper arenaceous and conglomerate beds of the Tatlayoco Lake sections, the discovery 

 of fossils on the Iltasyouco River, of a horizon close to though probably lower than that of the 

 Jackass Mountain group, together with additional evidence tending to show the blending of the 

 ordinary aqueous sediments of the upper part of the Jackass Mountain series with the igneous 

 products of the Porphyrite series, leaves httle room for doubt that the latter is the downward 

 continuation of the former, and that the whole constitutes a formation, bridging to some extent 

 the gap ordinarily found between the Cretaceous and Jurassic. 



Detailed sections and descriptions of these rocks, which exceed 2,000 feet in 

 thickness, are given on pages 59 to 72 of Dawson's report. 



Whiteaves ^" reports on the fossils from the "Porphyrite group" of Iltasyouco 

 River and closes with the following comment on correlation: 



The fossils above enumerated are of much interest as affording the first instance yet observed 

 of the occurrence of a well-marked fauna of Jurassic age in British Columbia. It is true that 

 fossils, probably from a very similar geological horizon, were collected by Mr. Selwyn in 1875, 

 at Rock Island Gates, below Hudson's Hope, on the Peace River, but these specimens, which 

 were described in the report of progress for 1875-76, are very few in number and so imperfect 

 that none of the species could be satisfactorily determined. 



