582 EDWARD STEIDTMANN 



UNCONFORMITY AT BASE OF CAMBRIAN 



Micaceous shaly sandstone uniform in composition 

 but varying in color. Ripple marked and cross- 

 bedded throughout. 2,297 feet thick. 

 Basal conglomerate, 6 feet 

 Unkar Group. Calcareous shales and dolomitic limestones and 



dolomites containing some ripple marks, sun- 

 Thickness, 478a feet. cracks; total thickness, 304 feet. 



Ripple-marked, cross-bedded jaspers, quartzitic 

 jasper, intrusive diabase, blue, red, vermilion, 

 argillaceous and arenaceous shales. Thickness 

 579 feet. 

 Pure fine-grained sandstones and quartzites, ripple- 

 marked and cross-bedded. 1,564 feet thick. 

 Unconformity. 



Vishnu series. Quartz schist, quartz mica schist, quartz hornblende 



schist, hornblende schist, quartz diorite and 

 pegmatite granite. 



Paige^ states that the pre-Cambrian complex of Grant County, 

 New Mexico, comprises various types of coarse-to-medium- 

 grained granites and porphyries, and pegmatitic dikes. 



Patton^ finds that the pre-Cambrian rocks of the Grayback 

 Mining district of Costilla Co., Colorado, consist of granite, 

 granite and biotite gneiss, and a small amount of hornblende schist, 

 amphibolite, and pegmatite. 



Pardee^ describes the sedimentary rocks of the Upper St. Joe 

 River in Idaho which are supposed to be equivalent to the Algon- 

 kian formations of the Coeur d'Alene district. They consist of 

 sandstones, graywackes, quartzites, shales, garnetiferous mica 

 schists, and limestone. 



Ransome^ states that the basal rocks of the Breckenridge district 



^ Sidney Paige, "Metalliferous Ore Deposits near the Burro Mountains, Grant 

 County, New Mexico," Bull. 470, 1911, U.S. Geological Survey (1911), pp. 131-50, 

 I map. 



^ H. B. Fatten et al., " Geology of the Grayback Mining District," Colo. Geological 

 Survey, Bull., 2, 1910, in pp., 9 pis. 



3 J. T. Pardee, "Geology and Mineralization of the Upper St. Joe River, Idaho,' 

 Bull. 470, 1910, pp. 39-61, I map. 



"tF. L. Ransome, "Geology and Ore Deposits of the Breckenridge District," 

 U.S.G.S., Prof. Paper 75, 1911, pp. 187, 



