ABSTRACTS 



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

 prepared and signed by themselves, are forwarded promptly to the editors. 

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

 this issue. 



GEOLOGY. — Oxidized zinc ores of Leadville, Colo. G. F. Loughlin. 

 U. S. Geological Survey Bulletin No. 68i. Pp. 91, pis. 8, figs. 7. 

 1918. 



Although deposits of oxidized zinc ores at Leadville, Colo., had been 

 exposed in mine workings for many years previously, it was not until 

 19 10 that their character and extent began to be realized. Since that 

 year large quantities have been mined annually. Bulletin 681 begins 

 with a review of early accounts of zinc carbonate and silicate and of 

 the recent discovery of the ore bodies. It then describes in detail the 

 oxidized zinc ore minerals and minerals associated with them, the 

 varieties of ore, their range in metal content, their distribution and 

 extent, and their genesis. G. F. L. 



GEOLOGY.— r/z^ evaporation and concentration of waters associated 

 with petroleum and natural gas. R. Van A. Mills and R. C. 

 Wells. U. S. Geological Survey Bulletin No. 693. Pp. 104, 

 pis. 4, figs 5. 1919. 

 The widely observed association of saline waters with petroleum and 

 natural gas is ascribed by the authors, at least in many cases, to deep- 

 seated concentration brought about by evaporation into moving and 

 expanding gas. During this concentration there is a definite order of 

 change in the relative proportions of the dissolved constituents in the 

 waters. Carbon dioxide and other gases are lost from solution. Cal- 

 cium, magnesium, and iron separate from solution as carbonates, and, 

 under favorable conditions, sodium chloride separates, — a process illus- 

 trated in the "salting up" of gas wells. 



In discussing these changes the authors present evidence based on 

 field studies as well as laboratory determinations, including the results 

 of examinations of the rock specimens, analyses of the waters, the 

 determination of the solubility of salt in solutions carrying calcium 

 chloride, the vapor pressure of water in illuminating gas, and a resum^ 

 of the initial gas pressures in several gas fields. Elaborate compar- 



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