120 DEPARTMENT OF THE INTERIOR 



2 GEORGE V., A. 19f2 



conformable sedimentary formations, each of which, on account of its homo- 

 geneity, as yet defies profitable systematic analysis into subdivisions of more 

 usual thickness. Even these grand divisions of the thick series, called the 

 Creston, Kitchener, and Moyie formations, are not always with ease separable 

 from one another in the field. All are highly silicious in character; all are 

 fine-grained to compact in texture; all show phases which are indistinguishable 

 in the hand specimen or in the ledge. The three formations are, in fact, 

 separated on the ground of comparatively subordinate lithological differences, 

 such as colours of fresh fracture and weathered surface. 



Microscopically and chemically the immensely thick Creston and Kitchener 

 formations are proved to be almost identical in constitution. A prevailing and 

 clearly minor difference between them, consisting in the fact that the Kitchener 

 is the more ferruginous of the two formations, has been used as a principal means 

 of distinguishing these two parts of the series in the field. In addition, the 

 Kitchener is thinner-bedded than the Creston. With such criteria merely, it is 

 clear that the mapping of these formations in the fault-riven mountain masses 

 is a delicate matter. The geological boundaries as shown on the map sheets 

 are thus to be considered as drawn, in many instances, with more doubt than 

 is the case with the sheets located east of Gateway. 



Two of the sedimentary formations have been named after stations on 

 the Canadian Pacific railway; the third, the Moyie formation is so called 

 after the river of that name. Their estimated thickness and general composi- 

 tion are noted in the following table : 

 formation. Thickness in feet. Dominant rocks. 



Top, erosion surface. 



Moyie 3,400+ Metargillite. 



Purcell Lava.. * 465 Altered basalt. 



Kitchener 7,400 Quartzite. 



Creston 9,500+ Quartzite. 



20,765+ 

 Base concealed. 



Creston Formation. 



General description. — The lowest member of the Purcell series and the old- 

 est formation seen in the Boundary belt within the entire Purcell mountain 

 system has been named the Creston formation. Its best exposures include the 

 one in and east of the lofty McKim cliff four miles from Porthill; a less com- 

 plete one on the slope immediately east of the Moyie river; and, finally, the 

 most favourable one of all, on the two sides of the wide valley occupied by the 

 east fork of the Yahk river. In each of these exposures the formation pre- 

 serves nearly constant characters to the lowest bed visible; it is thus highly 

 probable that this gigantic sedimentary formation is, as a whole, yet thicker 

 than the total mass actually measured in the field. 



In different sections among the fault-blocks characteristic of the Purcell 

 mountain system, estimates of from 6,000 to 9,909 feet were obtained for the 



