662 abstracts: geology 



tivity gave no reliable evidence of any effect attributable to the eclipse, 

 and, while the diurnal variation curves for the potential-gradient 

 showed depressions at the time of maximum obscuration, this effect 

 was not sufficiently pronounced, in relation to other variations, to 

 render its connection with the eclipse a certainty. W. F. G. S. 



GEOLOGY. — Notes on some mining districts in eastern Nevada. James 

 M. Hill. U. S. Geological Survey Bulletin 648. Pp. 207, with 

 6 plates and 18 figures. 1916. 

 This reconnaissance report describes 29 mining districts in eastern 

 Nevada, extending from the line of the Southern Pacific Railroad to 

 the Colorado River and comprising parts of Elko, White Pine, Lincoln, 

 Nye, Clark, and Lander counties. Details of the mining development 

 in the various camps are given, as well as information concerning the 

 production of those districts for which figures are available. The re- 

 port discusses briefly the grouping of the copper, lead, gold, and silver 

 deposits about or near masses of granitic rocks which are intrusive 

 into Paleozoic sediments ranging in age from Cambrian to Permian, 

 and of gold veins in the probably pre-Cambrian schists near the Colo- 

 rado River. It includes notes on the tungsten deposits in the Kern 

 Mountains of northeastern White Pine County, and on gold deposits 

 associated with Tertiary volcanic rocks at Atlanta, Lincoln County, 

 in which carnotite is found. Most of the deposits discussed are either 

 replacements or veins. Contact metamorphic deposits, though of some 

 importance, are not as common in this region as would be expected 

 from the wide distribution of intrusive rocks. J. M. H. 



GEOLOGY. — Geology and ground waters of northeastern Arkansas, with 

 a discussion of the chemical character of the waters. L. W. 

 Stephenson, A. F. Cruder, and R. B. Dole. U. S. Geological 

 Survey Water-Supply Paper 399. Pp. 315, with 11 plates and 4 

 figures. 1916. 

 The report describes the physiography, geology, and ground water 

 resources of that part of Arkansas lying northeast of Arkansas River 

 and east of the Ozark hills. Much information compiled from scattered 

 previously published sources is incorporated, together with a large 

 amount of new data gathered by the authors in the field and by corre- 

 spondence. Emphasis is laid on the availability of the vast quantities 

 of water contained in the Pleistocene alluvial deposits for the irriga- 

 tion of the extensive tracts of land that are suitable for rice culture. 



