REVIEWS 383 



est bedrock formation of the region. It is believed to be a greatly 

 metamorphosed series of "argillaceous and sandy shales, argillaceous 

 sandstones, and arkoses which represent a thickness of several thousand 

 feet." The associated igneous rocks are, in the order of decreasing 

 age, basic sheets and flows, granitic intrusives (batholiths with radiating 

 dikes of granite and pegmatite), basic intrusives, and granite and peg- 

 matite intrusives, a basic dike. The Manhattan schist apparently 

 overlies the Inwood limestone conformably. The Inwood-Manhattan 

 series is thought by Merrill, Dana, Mather, and others to be equivalent 

 to the Cambro-Ordovician Poughquag-Wappinger-Hudson River series; 

 it is believed by Berkey to be pre-Cambrian. 



V. O. T. 



The Constitution of the Natural Silicates. By F. W. Clarke. 

 U.S. Geol. Surv. Bull. No. 588. Pp. 128. 

 In the opening chapter the author outlines some of the bases upon which 

 structural formulae may lie, but in the remainder of the bulletin the structures 

 are worked out by simply matching valences in such a way as to agree with 

 the empirical formulae. Until our methods of synthesis are better worked out, 

 and the decomposition of silicates is better understood, it is difi&cult to justify 

 the speculative structures advanced, as they do not rest on a foundation of 

 experimental study, but rather on the more mathematical concept of valence 

 and chemical combination. 



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Our Mineral Reserves. By G. O. Smith. U.S. Geol. Surv. Bull. 

 No. 599. Pp.48. 



In response to a demand for information as to sources of various mineral 

 products the director of the Geological Survey has prepared this bulletin, 

 which deals with the general situation, and briefly summarizes the condition 

 of the industries producing some twenty-odd products. 



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The Darwin Silver-Lead Mining District, California. By Adolph 

 Knopf. U.S. Geol. Surv. Bull. No. s8o-A, pp. 1-18. Figs. 3. 



Some of the ore bodies in this region are of contact metamorphic origin, and 

 some are transitional; but most are fissure veins. For the most part, the ore 

 bodies are found in the "lime-silicate" rocks which are metamorphosed sedi- 

 mentary rocks. The deposits are of interest in that they show the transition 

 between contact metamorphic deposits and fissure veins. 



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