178 Reviews — Useful Minerals and Rocks. 



there is nothing, beyond the fact that many of the illustrations are 

 drawn from the collection of the Geologische Landesanstalt in Berlin, 

 to suggest the original foreign source. He has been at great pains to 

 study the precise meaning of the technical words, and in his preface 

 gives an interesting essay on the subject. The German word Gang, 

 for instance, may be translated as either ' lode ' or ' vein' ; the latter 

 has a similar sense to the former, but is of a less important character, 

 though, it is pointed out, the meaning has been somewhat confused 

 by the vagaries of American Law phraseology. 



The first volume includes five principal parts : viz. on ore- 

 deposits in general, magmatic segregation, contact-deposits, tin-lodes, 

 and quicksilver lodes. Neither the parts nor the chapters comprising 

 them are numbered. The first part occupies nearly half the volume, 

 and includes such important chapters as those on classification, form 

 and graphic representation of ore-deposits, mineral formation, the 

 relative distribution of the elements and their natural associations 

 with especial reference to the metals, the origin of ore-deposits, the 

 absolute and the relative amounts of the metals in useful ore-deposits, 

 primary and secondary depth-zones, indications of ore-deposits at the 

 surface, and the scientific classification of ore-deposits. A conspicuous 

 and important feature of the book is the excellent bibliography that 

 heads each section, the student being thereby placed in touch with all 

 the principal books and memoirs written on the subject in question. 



Probably the reader already acquainted with the subject will first 

 look to see what classification has been adopted by the authors. 

 Many systems have from time to time been suggested, all of which 

 are referable to three different types, viz. according as they are 

 based upon the shape, the content, or the genesis of the deposit. The 

 first has much to commend it from the practical mining, and the 

 second from the commercial point of view, but neither can be 

 defended on scientific grounds, and the third alone remains. Like 

 most recent writers, the authors adopt a classification based upon 

 Stelzner's and divide deposits into two main groups — the syngenetic, 

 ores formed contemporaneously with the rocks surrounding them, 

 and the epigenetic, ores formed subsequently. In a later chapter 

 they put forward a complete scientific classification consisting of four 

 main groups: I, magmatic segregations; II, contact deposits ; 

 III, cavity fillings and metasomatic deposits; IV, ore beds. In 

 a second edition they will no doubt include some reference to the 

 highly interesting and cogent paper which Mr. T. Crook, of the 

 Imperial Institute, read before the Mineralogical Society, and 

 published in the Mineralogical Magazine last July. In it he considers 

 the classification of rocks, regarding ore-deposits rightly as only 

 a special case of the problem, and points out grave objections to all 

 the existing schemes of classification. For instance, Stelzner's main 

 groups often unite the different and separate the similar ; to quote 

 Mr. Crook, " Thusore deposits resulting from igneous activity may 

 be either ' syngenetic ' or ' epigenetic ' ; the ' syngenetic ' group 

 includes both igneous segregations and sedimentary deposits; and 

 vein deposits are ' epigenetic ' whatever may have been the origin of 

 the solutions from which they have been deposited." He himself 



