SOME PRE-CAMBRIAN LITERATURE OF NORTH AMERICA 577 



Bancroft^ states that the oldest rocks in Northern Yuma 

 County, Arizona, are granites and diorites, probably of Archaean age. 

 They are capped by a thick series of metamorphosed pre-Cambrian 

 sediments, quartzites, limestones, dolomites, argillites, arenaceous 

 shales, and quartz mica schists, interlay ered and intruded by basic 

 rocks altered to amphibolites. 



Blackwelder^ reports that the pre-Cambrian of three geologic 

 sections in western Wyoming consists of gneiss, gray, and red 

 granites penetrated by diabase and other dikes, hornblende gneiss, 

 and granite with large dikes of diabase. 



Blackwelder^ states that the pre-Cambrian rocks of the Laramie 

 and Sherman quadrangles of northeastern Wyoming include: 

 (i) hornblende schists, associated with some schistose rhyolites and 

 felsites, soft mica gneisses et cetera, and rocks resembling contorted 

 quartzites, and limestones, all highly metamorphosed; these rocks 

 are the oldest in the area; (2) mildly metamorphosed granite 

 gneiss representing two periods of intrusion, both younger than (i); 

 (3) basic intrusives, comprising syenites, gabbros, diorites, grano- 

 diorites, and gabbro gneiss, all younger than (2) ; (4) granite por- 

 phyry intrusive into (i) and (2); (5) anorthosite, intrusive into (i), 

 (2), and the gabbro gneiss of (3); (6) granite intrusive into (i), (2), 

 (3), (4), and (5); (7) small diabasic and dioritic dikes injected into 

 (6) and probably younger than (7). 



Blackwelder'' finds an unconformity in Big Cottonwood Canyon 

 along the upper course of the Ogden River in the Wasatch Moun- 

 tains, between shghtly fossiliferous early Cambrian quartzites and 

 an older quartzite slate series, several thousand feet thick, which he 

 assigns to the Algonkian in accordance with the prevailing methods 

 of correlation. 



' Howland Bancroft, "Reconnaissance of the Ore Deposits in Northern Yuma 

 County, Arizona," BiM. 451, U.S. Geol. Survey, 1911, pp. 130, maps and illustrations. 



^ Eliot Blackwelder, "A Reconnaissance of the Phosphate Deposits in Western 

 Wyoming," Bull. 470, U.S. Geol. Survey, 1911, pp. 452-81. 



3 N. H. Darton, E. Blackwelder, C. E. Siebenthal, "The Laramie and Sherman 

 Quadrangles, Wyoming," U.S. Geol. Survey, Folio No. 173, 17 pp., 8 pis., 3 figs. 



"t Eliot Blackwelder, "New Light on the Geology of the Wasatch Mountains, 

 Utah," Bull. Geol. Soc. Am., XXI (1910), 517-42, pis. 36-40. 



