38 abstracts: geology 



along the contact of the granite with the schists and gneisses. They 

 are valuable for their lead-silver content and have yielded the principal 

 output. The replacement deposits occur principally in a small area 

 at the northern end of the Conconully district. They contain small 

 amounts of copper and gold, but no ore has yet been produced com- 

 mercially from them. R. W. S. 



GEOLOGY. — A reconnaissance of the Archean complex of the Granite 



Gorge, Grand Canyon, Arizona. L. F. Noble and J. Fred. 



Hunter. U. S. Geological Survey Professional Paper No. 98-1. 



Pp. 95-102, with 1 plate and 2 figures. 1916. 



The Tonto platform on the south side of the Granite Gorge affords 



a magnificent but difficultly accessible cross-section through the 



Archean complex, 800 feet deep and 40 miles in length. These oldest 



rocks of the Grand Canyon were visited in twenty localities, 67 hand 



specimens were collected, and eight distinct groups of rocks were 



recognized. The exposures within these groups are described and the 



petrography of the specimens is given. 



Estimated roughly, the gneisses (granite gneiss, hornblende gneiss, 

 and metabasite) comprise 50 per cent of the rock exposed in the Gran- 

 ite Gorge; the mica schist, 30 per cent; the basic intrusives, 10 per 

 cent; and the pink siliceous intrusives, 10 per cent. It is not im- 

 probable that the mica schists are in large part of sedimentary origin. 

 It is believed that some of the wrinkled and contorted granite gneisses 

 represent the original basement on which the schist series of meta- 

 morphosed sediments was laid down; that both before and after the 

 deposition of the sediments there were long periods of complex intru- 

 sion, represented by amphibolites, granitic gneiss, metabasite, and 

 metadiorite; that during and after the metamorphism of the schists 

 and gneisses there were further intrusions of quartz diorite, gabbro, 

 granite, pegmatite, and other rocks. It will probably be advisable, 

 at some future time, to restrict the name "Vishnu schists," now used 

 for the entire Archean complex, to the mica-schist series and give 

 another name or names to the gneisses. J. F. H. 



GEOLOGY. — An anticlinal fold near Billings, Noble County, Oklahoma. 



A. E. Fath. U. S. Geological Survey Bulletin 641-E. Pp. 121- 



138, with 1 plate. 1916. 

 During February, 1916, gas was struck in small quantities at shallow 

 depths in a well being drilled a few miles southwest of Billings, Noble 



