Reviews — Ore Deposits, Rossland, British Columbia. 39 



importance is to be deprecated, while the beautifully simple 

 diagrammatic representation of the successive occurrence of water, 

 oil, and gas in the arched strata is at its best but a crude and partial 

 statement of the whole story. 



The tendency of modern investigation has been to prove that the 

 original nidus of the hydrocarbons is the fine-grained sediments, and 

 that the migration into the coarser and permanently more porous 

 horizons takes place at an early stage as the result of compacting. 

 Many of these porous horizons are quite limited in their lateral 

 extent, so that the later migration as a result of tilting and folding 

 movements is often limited, unless abnormal conditions such as 

 faults and joints produce planes of egress for the gas or oil. Hence 

 it is found that as a result of variations in porosity and of irregular 

 deposition of sandy horizons, the primary migration due to com- 

 pacting is often of more importance in the differentiation of oil into 

 pools than the later earth movements, which merely localize the oil and 

 gas in the higher portions of the more porous strata. Of course, in 

 many cases, the coarse horizons are sufficiently widespread to allow the 

 anticlinal hypothesis to hold, but the reverse is more common in 

 nature than is usually suspected. - 



V. C. I. 



VII. — Gkologt and Ore Deposits of Rossland, British Columbia. 

 By Charles Wales Drysdale. Memoir 77 of the Geological 

 Survey. Ottawa, Government Printing Bureau, 1915. pp. xiv 

 + 317, with 8 maps in pocket, 25 plates, and- 26 figures in the 

 text. 



^HE rich district of Rossland, which is situated in the Trail Creek 



T 



Columbia, about 6 miles west of Columbia River and 5 miles north 

 of the International Boundary, produces gold, silver, and copper. 

 It was discovered in 1890, and has been worked continuously since 

 1894. In this memoir the region is very fully described. The 

 geological features and the mineral enrichment, which present many 

 points of interest, are discussed in some detail. The district appears 

 to have been covered by sea during at least part of the Carboniferous 

 age, and upheaved at the end of the Palaeozoic era. An intrusion of 

 augite porphyry occurred during the Triassic period, and at the close 

 of the Jurassic period the rock formations were invaded by the Trail 

 granodiorite batholith, this being the first period of mineralization. 

 Erosion took place throughout Cretaceous times, and at the end the 

 whole Cordillera was uplifted and the present ranges were outlined. 

 The second main period of mineralization occurred in Miocene time. 

 During the Pleistocene a change to a glacial period took place. 

 The ore consists of pyrrhotite, chalcopyrite, pyrite, and marcasite, 

 with a little arsenopyrite, molybdenite, and bismuthinite, in a 

 gangue of altered country rock, containing some quartz and locally 

 a little calcite. The deposits resemble in many respects the well- 

 known ones atNamaqualand, Cape Colony, and possess some structural 

 features in common with those at Butte, Montana. 



