372 DEPARTMENT OF THE INTERIOR 



2 GEORGE V, A. 1912 



tion the writer is inclined to recognize three periods of strong mountain-build- 

 ing for these mountains; one, late Jurassic; a second, post-Lararnie and pre- 

 Miocene; the third, late Miocene. Each period seems to have been immediately 

 followed by batholithic intrusion. Apart from the Cretaceous and earlier 

 vulcanism, as well the important erosion-periods registered in the unconform- 

 ities, the structures of the Rossland mountains are largely explained by the 

 grand events just enumerated. So far as recorded in the exposed rocks the 

 region appears to have been above sea since Carboniferous times, though at 

 any time discoveries may show the presence of Mesozoic or Tertiary marine 

 strata in the volcanic complex.* Meantime, it can be stated that this mountain 

 group owes its principal structures to the repeated orogenic crushing of a very 

 heavy volcanic pile and of its metamorphosed Paleozoic foundation. 



Time Relations. 



With present knowledge, the chronicle of geological events in the Rossland 

 mountains can be only partially deciphered. The difficulties in the way of 

 completing a systematic survey of their history are the usual ones encountered 

 in the Boundary survey as, indeed, in most areas of complex mountains. 

 Imperfect exposures, the rarity of sedimentary formations and the even more 

 notable scarcity of fossils form part of the difficulties, but the great variety and 

 obscure relations of the igneous rock-bodies, both extrusive and intrusive, are 

 responsible in special degree for the uncertainties still affecting the geology of 

 these mountains. A tentative scheme of the geological events will be offered in 

 the present section. . The grounds on which the scheme is based belong to three 

 classes: first, those which may be rated as observed facts; secondly, those which 

 are regarded as more or less strong probabilities; and, thirdly, those which are 

 to a large extent theoretical, embodying principles derived from other fields. 



Observed Facts. — It is convenient to survey the known facts of relation in 

 outline, as follows. Certain of the associated probabilities will be noted in 

 direct connection with these statements. 



1. The crystalline limestone of Little Sheep creek valley and a' bed of 

 calcareous quartzite at the O.K. mine west of Rossland are obscurely fossilifer- 

 ous. The limestone is crinoidal and is lithologically similar to that occurring as 

 fragments in the volcanic breccia of Sophie mountain. In those fragments 

 McConnell found fossil remains which have been regarded as probably of 

 Carboniferous age. All these limestones are lithologically similar to the Pend 

 D'Oreille limestone across the Columbia river. The fossils discovered by Brock 

 in the O.K. mine quartzite are tentatively referred by Ami to the Car- 

 boniferous. 



2. The much less metamorphosed Sophie mountain conglomerate, and the 

 argillite-sandstone series occurring at the crossing of Little Sheep creek and 

 the Boundary line are also f ossilif erous ; in each case the remains are those of 



* Tbe more massive phases of the Rossland volcanic group resemble the Nicola 

 Triassic lavas on the South Thompson river. 



