±66 Scientific Intelligence. 



In this book, Mr. Johnson has made an important addition to our 

 limited knowledge of prehistoric South Africa. u. e. g. 



6. Ore deposits of the Stive?' Peak Quadrangle, Nevada • by 

 Josiah Edward Spurr. U. S. Geol. Survey, Professional Paper 

 No. 55. Pp. 174, 24 pis., 40 figs, in text. — The sedimentary rocks 

 of the Silver Peak quadrangle include a thick series of limestones, 

 slates and quartzites, of Paleozoic age, with shales, sandstones, 

 tuffs and interbedded lava flows of Tertiary time. There are 

 abundant intrusions of granitic rocks which pass into alaskites 

 and by diminution of feldspar into pure quartz veins. The vari- 

 ous phases of the granitic intrusions are regarded as derived from 

 a single granitic magma, and represent a single period of intrusion. 



An intimate interrelation has been recognized for all the metal- 

 liferous ores of the quadrangle, and all have been traced to the 

 consequence of the intrusion of granitic rocks into Paleozoic sed- 

 iments. The ore deposits may be divided into two chief groups, 

 (1) bodies of auriferous quartz which separated out from alaskite 

 during the process of cooling ; (2) quartz veins due to replace- 

 ment or impregnation of original material along fracture zones 

 by siliceous solutions more attenuated than those which deposited 

 the ores of the first type and probably residual from the crystal- 

 lization of the magmatic quartz of the first type. These depos- 

 its contain relatively more gold when they occur in the granite 

 and more silver and lead when they occur in the sedimentary 

 rocks. Their different character under these conditions is believed 

 to be due largely to the difference in the wall rocks, w. e. f. 



7. Geology and Gold Deposits of the Cripple Creek District, 

 Colorado / by Waldemar Lindgren and Frederick Leslie 

 Ransome. TJ. S. Geol. Survey, Professional Paper No. 54. Pp. 

 496, 29 pis., 64 figs, in text. — The Cripple Creek gold deposits, 

 discovered in 1891, were investigated by Cross and Penrose in 1894. 

 The extensive developments in the district since that time ren- 

 dered a resurvey of the district desirable. New maps have been 

 prepared and a detailed stud}'' of the rocks and ore deposits of the 

 district is presented in this paper. The following are the most 

 important modifications of the views presented in the original 

 paper : 



The various volcanic rocks of the district are proven to have 

 very close genetic relations with each other, and in many cases 

 are found to be so closely connected by intermediate types as to 

 be practically inseparable. None of the massive rocks can be 

 properly called andesites, and the volcanic breccia, usually spoken 

 of as "andesitic breccia," is rather composed chiefly of fragments 

 of phonolitic rocks accompanied locally by much granite, gneiss, 

 or schist detritus. 



None of the massive rocks erupted from the Cripple Creek vol- 

 canic center show any evidence of being surface flows. They 

 are for the most part intrusive porphyries, ranging from nephe- 

 line-syenite to the aphanitic phonolite of the dikes. The breccia 

 in the main fills a steep walled chasm extending to unknown 

 depth and constitutes a typical volcanic neck. 



