724 REVIEWS 



in the sediments should presumably have been less uniform over wide 

 areas than is actually the case. 



The author of the paper turns therefore to igneous sources for an 

 explanation of the ores. He points out that the Permian intrusive rocks 

 of Europe are very generally copper-bearing and attributes the primary 

 deposition of copper in the Mansfield deposits to solutions coming from 

 the same magmatic source that at an earlier period yielded the eruptive 

 rocks that form part of the Rotliegende. Cupriferous mineralizing 

 solutions, according to Beyschlag, ascended along the vein fractures 

 and spread laterally through and beneath the copper shale depositing 

 chalcopyxite in the sediments by the filling of pores and by replacement, 

 the bitumen and pyrite in these beds being instrumental in the ore pre- 

 cipitation. They also deposited chalcopyrite, cobalt, and nickel arse- 

 nides, molybdenite and rarely pitchblende in the fault fractures. 



The writer points out that mineralization in the copper shale and 

 Zechstein is greatest where veins cutting these formations are numerous 

 and close together. 



Although Beyschlag does not emphasize particularly the genetic 

 significance of primary mineral composition, to the reviewer the presence 

 in the veins of cobalt and nickel arsenides, of molybdenite and of pitch- 

 blende is highly suggestive of a magmatic origin for the mineralizing 

 solutions. 



Of the primary ores developed by the processes just described only 

 remnants now remain. Most of the primary ore minerals have been 

 replaced by the rich copper minerals, bornite and chalcocite, through the 

 agency. Professor Beyschlag believes, of descending meteoric waters — 

 the familiar process of downward sulphide enrichment. As evidence of 

 such enrichment, it is shown that much if not most of the bornite and 

 chalcocite is a replacement of chalcopyrite and drawings are presented 

 showing such replacements. Bornite is characteristically the first 

 mineral to replace chalcopyrite; chalcocite then replaces bornite. Fur- 

 ther, there is a marked falling off in the abundance of the rich copper 

 minerals in depth. 



Of fundamental importance is the conclusion that the ores in the 

 sediments and in the veins were formed contemporaneously, a conclusion 

 based mainly on the restriction of ore in the veins to the vicinity of the 

 ore-bearing beds and conversely the greater development of ore in the 

 beds where they are cut by numerous and close-spaced veins. 



E. S. Bastin 



