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GEOLOGY. — Ore deposits of the northwestern part of the Garnet Range, 

 Montana. J. T. Pardee. U. S. Geological Survey Bulletin 

 660-F. Pp. 80, with 4 plates and 10 figures. 1918. 



The report describes the quartz lodes and placer gravels and the 

 principal features of the physiography and the geology in an area of 

 about 400 square miles north of Clark Fork River and east of Missoula. 

 The lodes are considered by districts, those of the Garnet, Coloma, 

 and Elk Creek districts, which are valuable chiefly for gold, being classi- 

 fied as filled fissures and replacement veins in granodiorite and schist. 

 In the Top o'Deep district there are contact-metamorphic replacements 

 in limestone valuable for copper, and quartz veins that contain gold. 

 In the Copper Cliff district mineralized fault breccias, and in the Clin- 

 ton district composite veins or shear zones in granodiorite, are valuable 

 for copper. Outlying deposits consist in part of silver-bearing galena 

 that has replaced limestone. 



Under placer deposits is given a brief historical sketch of Bear and 

 Elk creeks, which produced between $6,000,000 and $10,000,000 in 

 placer gold in the "early days," and the origin of the gold-bearing 

 gravels is discussed. 



Under geology there are condensed descriptions of the rocks, which 

 include 5000 feet of Belt strata, chiefly quartzite and shale; 4000 feet 

 of Paleozoic strata, mostly limestone; early Tertiary or late Cretaceous 

 intrusive granodiorite; and middle Tertiary extrusive rocks. Folds 

 and faults involve the strata, one of the chief structural features being 

 a large overthrust fault that has carried a great mass of Belt rocks 

 from the west over Paleozoic and younger formations. 



Under physiography the elevated remnants of a peneplain are de- 

 scribed and their correlation with an erosion surface of Eocene age 

 known in the adjacent regions is indicated. 



J. T. P. 



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