ABSTRACTS 



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GEOLOGY. — Mineral resources of southwestern Oregon. J. S. Diller. 

 U. S. Geological Survey Bulletin 546. Pp. 147, 11 plates, 26 

 figures, maps, sections, and views. 1914. 



The rocks of southwestern Oregon, the northern portion of the Kla- 

 math Mountains, with a northeast strike toward the Blue Mountains 

 are pre-Devonian, Devonian, Carboniferous, Jurassic, Cretaceous, and 

 Eocene to Pleistocene inclusive. Paleozoic and Mesozoic lavas and 

 intrusives, including greenstones, serpentines, granodiorites, and a 

 variet}' of dike rocks cut the crushed sediments. The fissuring was 

 general instead of being concentrated in narrow belts. The final veining 

 of the rocks and the accompanying ore deposition formed many small 

 though commonly rich ore bodies instead of a few large ones. 



The deep weathering of the rocks durmg the late Mesozoic and Ter- 

 tiarj'- concentrated the heavier metals in the residual mantles that gave 

 much to the auriferous gravels of (1) the invadmg Cretaceous sea 

 (beaches) encircling the Klamath Mountains, (2) the enlivened streams 

 of the Klamath Peneplain, (3) streams of the Sherwood Peneplain, and 

 (4) streams of today. Under favoring conditions the deep weathering 

 of the later geologic periods ma}^ have contributed to the secondar}^ 

 enrichment of the ''pockety deposits" for which southwestern Oregon 

 is well known. 



The overturning of the folded strata and the overthrust of the Devo- 

 nian upon the Jurassic toward the sea on the northwest is apparently 

 a fundamental structural feature of the Klamath Mountains. J. S. D. 



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