Reviews 



The Ore Deposits of New Mexico. By Waldemar Lindgren, 

 Louis C. Graton, and Charles H. Gordon. Professional 

 Paper 68, U.S. Geological Survey, 1910. Pp. 361. 



This paper treats a subject about which most geologists have known 

 comparatively little, and of which most of us are eager to learn. 

 Although some of the mining districts were worked by the Spaniards 

 long before the United States became a mining nation, the geology and 

 ore deposits of the state are less well known, perhaps, than those of 

 any other portion of the country. During the past decade several 

 papers treating the deposits of large areas have appeared, and these, 

 the reviewer believes, have contributed fully as much to the science of 

 economic geology as the more intensive studies of small areas. The 

 reconnaissance method of study and treatment gives a perspective which 

 detailed work of small and more or less isolated mining districts could 

 never do. This paper is the most comprehensive and in its scientific 

 aspects should be the most useful of its class. The deposits are so 

 varied and their genesis so clearly discussed that the student of ore 

 deposits will find the paper to possess the essentials of a textbook of 

 mining geology. 



Pre-Cambrian rocks do not occupy large areas in New Mexico; 

 the largest masses are found in the north and constitute the southern 

 extension of the Sangre de Cristo Range of Colorado. This belt ends 

 some 20 miles south of Santa Fe. Several other, smaller areas of pre- 

 Cambrian rocks are described. The pre-Cambrian rocks consist of 

 quartzites, mica schists of clastic origin, and some limestones. These 

 are intruded by normal granite, which in turn has been intruded by 

 masses and dikes of dioritic rocks. The latter are at some places cut by 

 pegmatite dikes and by a later granite. Schistosity in varying degrees 

 has been produced in both the sedimentary and the igneous rocks. 

 At some places the granite breaks through or contains remnants of older 

 greenstone tuffs, amphiboles, and rhyolites. The pre-Cambrian sedi- 

 mentaries probably correspond in age to those imbedded in red granite 

 in various places in Colorado. Perhaps they should be correlated also 

 with the quartzitic Pinal schists of southeastern Arizona. 



The pre-Cambrian history, one of sedimentation, mountain build- 

 ing, and igneous intrusion, was followed by long-continued erosion, 



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