ABSTRACTS 



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GEOLOGY. — Geology and mineral deposits of the Colville Indian Reser- 

 vation, Washington. J. T. Pardee. U. S. Geol. Survey Bull. 

 677. Pp. 1 80, 12 plates and i figure. 1918. 



The rocks exposed are the Covada group which consists of schistose 

 argillite, greenstone, and limestone of probable Carboniferous age; the 

 intrusive Colville granite probably Cretaceous ; dike rocks and lavas of 

 Tertiary age; and Pleistocene glacial deposits. 



The Pleistocene Cordilleran Ice cap overran all the Reservation 

 except part of San Poil Valley. After the ice had withdrawn the valley 

 of Columbia River was ponded to the present 1700 foot contour. This 

 water body was displaced by the Nesplem Silt from which the river 

 carved terraces as it re-excavated its channel. The Nesplem Silt is 

 correlated with the White Silt formation of Dawson in Frazer valley, 

 British Columbia. 



The mineral deposits consist chiefly of veins that contain silver, lead, 

 and zinc and contact metamorphic deposits valuable mainly for copper. 

 Most of the known lodes of economic importance are confined within 

 four more or less definite area near Nesplem, Park City, Covada, and 

 Keller. With respect to roek formations, the lodes are about equally 

 divided between the Colville granite and the Covada group. No metal- 

 bearing lodes have been found in rocks younger than the Colville 

 granite. Most of the veins are narrow, the oxidized zone is shallow, 

 and secondary enrichment, though conspicuous in one or two mines, is 

 not common. Some of the contact metamorphic deposits are large 

 but of very low grade. J. T. P. 



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