ABSTRACTS 



Authors of scientific papers are requested to see that abstracts, preferably 

 prepared and si^ed by themselves, are forwarded promptly to the editors. 

 The abstracts should conform in length and general style to those appearing in 

 this issue. 



GEOLOGY. — Deposits of manganese ore in Nevada. J. T. Pardee 

 and E. L. Jones, Jr. U. S. Geol. Survey Bull. 710-F. Pp. 34 

 (109-242), pi. I, figs. 2. 1920. 



The report describes between twenty and thirty deposits rather 

 generally distributed over the State of Nevada, from which about 

 25,000 tons of manganese ore were produced during the war. Under 

 the head of "Deposits formed by replacement of country rock by car- 

 bonate or silicate minerals that have become partly or completely 

 oxidized," are described the Siegel mine, near Schellboume, and several 

 deposits elsewhere, that show a characteristically cavernous texture 

 in the oxidized zone and are dense below it, where they consist largely 

 of carbonate and silicate of manganese. Like the metalliferous quartz 

 lodes of the surrounding region, to which these bodies are closely re- 

 lated, their origin is ascribed to solutions ascending from intrusive 

 magmas. 



Deposits formed by replacement of country rock by oxide minerals, 

 as typified by the Three Kids deposit near Las Vegas, consist largely 

 of somewhat porous but not cavernous masses of wad and other soft 

 oxides. The origin of the manganese is obscure in these and in several 

 bodies near Golconda that are classified as silicate and carbonate 

 lenses in metamorphic rocks. 



Minerals of special interest mentioned in the report are alabandite, 

 a sulfide of manganese which is found rather plentifully in the Siegel 

 mine, and exceptionally bright colored rhodonite that is abundant in 

 the O'Brien and Tucker deposit near Golconda. J. T. P. 



GEOLOGY. — Deposits of manganese ore in Costa Rica and Panama. 

 J. D. Sears. U. S. Geol. Survey Bull. 710-C. Pp. 31 (61-91), 

 pi. I, figs. 28. 1919. 



During the war the Geological Survey investigated deposits of ore 

 of metals used in the manufacture of ferro-alloys, pig iron, and steel, 

 and made estimates of tonnage available as substitutes for foreign 

 ores. This paper describes forty deposits of manganese oxide in the 



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