August 26, 1909] 



NA TURE 



24: 



ifjneous rocks. It summarises the characters of the 

 chief rock-forming minerals, and of the origin and 

 classification of rocks, and is illustrated by an admir- 

 able series of photographs and diagrams showing the 

 field relations of igneous rocks. The author makes a 

 useful protest against the appropriation by geologists 

 of popular rock names in new and technical meanings. 

 1 he term granite, for example, is used in the stone 

 trade in its correct historical and etymological sense, 

 which is entirely different from its use in geology. 

 This system is as inconvenient, as Prof. Pirsson 

 points out, as if botanists had re-defined the terms 

 bush, tree, and shtub, limiting each to a particular 

 species. Prof. Pirsson 's protest is justified, and 

 though some American geologists are using the 

 familiar terms in their popular meanings, this reform 

 has probably been proposed too late. 



(2) Mr. Brenton Symons's " Genesis of Metallic 

 Ores and the Rocks which Enclose Them " is also 

 intended to appeal to the general elementary student, 

 and is an attempt to explain the formation of ore 

 deposits free from unnecessary technicalities. It is a 

 book, however, of very different standard from Prof. 

 Pirsson's; it is written by a practical engineer, who is 

 keenlv interested in the theoretical study of mining 

 geologv, but whose knowledge of the subject is a little 

 unequal. 



The book begins with a general introduction on 

 geological principles, followed by a section on rock 

 nietamorphism ; the third part of the book deals with 

 the ore deposits. Though the author avoids so far as 

 possible technical scientific terms, his text is often 

 repellent by the abundant use of such Americanisms 

 as cavations for spaces, such reformed spellings as 

 " lentiles " for " lenlicles," and vegetal for vegetable, 

 and mining terms of only local value. The most 

 valuable part of the book is its collection of diagrams 

 of ore occurrences ; the instances drawn from Corn- 

 wall are the most satisfactory, for some of his 

 diagrams and views regarding ores in other parts of 

 the world are a little out of date. Mr. Symons takes, 

 moreover, an extreme position as to the genesis of 

 ores. He has a great belief in the agency of 

 geosvnclinals, bv which sediments are carried down 

 to depths where they are melted, and then forced to 

 re-ascend as igneous rocks into overlying strata ; and 

 though he describes many ores as plutonic, he appears 

 to regard the vast majority of ores as having been 

 derived from the destruction of Archaan rocks and 

 precipitated in the sea. He says, on p. 3S1, " It has 

 been already observed that nearly all the ores that can 

 come within the reach of man have been derived from 

 the .Archean strata"; from these rocks, according to 

 Mr. Symons, the metals are removed in solution and 

 " precipitated on the bottom of the sea by chemical 

 reactions that were principally set up by organic 

 matter." He has no doubt, for example, that the 

 gold in the reefs of Nova Scotia and the copper ores 

 of Mansfeld were deposited in the rocks of those 

 mining fields during their deposition in the sea. His 

 view of the origin of crystalline rocks of most ores is 

 shown by the following quotation. 



" The presence of such minute proportions in all 

 formations is natural, since the crystalline rocks, as 



NO. 2078, VOL. Si] 



far as known, were originally_ deposited as marine 

 strata, and, consequentlv, retain some part of the 

 minerals that were precipitated during sedimentation 

 from the oceanic waters. The proportion of these 

 metals appears to be just the same, whether districts 

 are metalliferous or not " (p. 363). 



This extract shows that the author adopts such an 

 extreme position in regard to the genesis of ores that 

 his book must be read with caution. 



ZOOLOGlCkL PRIMERS. 

 (i) Die Saugetiere Dciitschlauds. By Dr. C. Hen- 

 nings. Pp. 174. (Leipzig: Quelle und Meyer, 

 1909.) Price 1.23 marks. 



(2) Korallcn und anderc gcstcinshildende Tiere. By 

 Dr. Walther May. Pp. iii+122. (Leipzig: B. G. 

 Teubner, 1909.) Price 1.25 marks. 



(3) Die Fortpflaiiziiiig der Tiere. By Dr. R. Gold- 

 schmidt. Pp. iv-l-124. (Leipzig: B. G. Teubner, 

 1909.) Price 1.25 marks. 



(4) Die Stammesgeschichte iinserer Haiistiere. By 

 Prof. Dr. T. Keller. Pp. iii4-ii4. (Leipzig: B. G. 

 Teubner, 1909.) Price 1.25 marks. 



(5) Biology. By Prof. R. J. Harvey Gibson. Pp. viii 

 + 120. (London: J. M. Dent and Co., 1909.) 

 Price IS. net. 



(i) '"p'HE most useful portion of this sketch of the 

 1 mammalia of Germany lies in the synoptic 

 tables placed at the head of each order ; but these 

 can hardly be considered as complete, since they do 

 not include any account of the subspecies, which are 

 of the greatest interest. 



A complete list prefixed to this book would have 

 made comparisons with the fauna of other countries 

 a much easier matter. As it is, one has to search 

 through the index in order to discover what forms 

 are included in this work. 



(2) Dr. May is a well-known writer on the anatomy 

 of corals, and in this little work he brings together 

 descriptions of a heterogeneous assemblage of 

 animals, the common feature amongst which is the 

 property of producing a hard exoskeleton, or of con- 

 tributing otherwise by their remains to the formation 

 of strata. 



The question inevitably arising out of this treatment 

 is. What determines the difference between, say, a 

 soft anemone and an encrusted coral? To this Dr. 

 May has, so far as we can see, no answer. Never- 

 theless, his book contains a good slcetch 01 the 

 various hypotheses accounting for the origin and 

 formation of coral-reefs, and for this, if for nothing 

 else, it is welcome. The corals and lamellibranchs 

 appear to us the best parts of the work. 



(3) Dr. Goldschmidt has undertaken to compress 

 into a hundred small pages an account of the methods 

 of animal reproduction, with especial reference to the 

 number of the young, their state on hatching, their 

 habits and adaptations. The work cannot be con- 

 sidered as really up to date, but the treatment is 

 interesting, and the subject is one of such importance 

 that' we regret more space could not have been. allotted 

 to it. The illustrations are better than those of any 

 other booklet of this series we have so far seen. : 



(4) In an earlier and larger work, published some. 



