5o6 



NATURE 



{April 27, 1876 



has exercised a very wise discretion. In these final 

 chapters the reader will find an excellent summary of the 

 latest contributions to Cosmogony, and a generally fair 

 and impartial discussion of the bearing and value of 

 recent geological theories. 



Of the suitability of Prof. Green's work as a text-book 

 for " students," we regret to say that we cannot speak so 

 favourably. The ability and enthusiasm with which our 

 author writes on certain portions of his subject, fail to 

 reconcile us to his inadequate treatment and sometimes 

 total neglect of others of equal importance ; and, in 

 perusing the book, it is impossible to avoid the feeling 

 that the space devoted to the several subdivisions of the 

 science must have been determined, not as the result of a 

 judicial consideration of their respective claims, but 

 almost entirely by the author's peculiar predilections. For 

 example, it is rather startling to find in ajwork on Physical 

 Geology, extending to 540 pages, no discussion what- 

 ever of the phenomena and origin of mineral veins, and 

 onlv, indeed, an incidental mention of their existence ! 



A still more serious blemish of the work, considered 

 as a student's manual, is the looseness of description and 

 inaccuracy of language in certain parts of it. This defect 

 is mist conspicuous in the second chapter, which treats 

 of the characters and classification of rocks, and which 

 offers a painful contrast to those later chapters of which 

 we have already spoken. Among the numerous grave 

 errors which every petrologist will remark in this chap- 

 ter, we may call attention to the following. In the enu- 

 meration of the principal crystallographic forms the 

 author omits such commonly occurring ones as the penta- 

 gonal-dodecahedron, the icositetrahedron, the scalenohe- 

 dron, and the tetrahedron, although some of these have 

 to be referred to in subsequent pages of the work ; of the 

 hetnihedral forms, indeed. Prof. Green makes no mention 

 whatever. We are told that when a piece of calc-spar is 

 broken up, " the shape of the fragments will be identically 

 that of the block we started with." Again, we read, in refer- 

 ence to the subject of Polymorphism, " This is spoken of 

 as Dimorphism, when the different crystalline shapes are 

 two in number ; Trimorphism when they are three in 

 number, and so on." The italics are our own. In speak- 

 ing of the constituents of a rock, the author places side 

 by side metals and oxides in the loosest manner, and 

 while the formula of soda is written NagO, that of potash 

 stands as KO. Olivine is classed as a mineral of the 

 augite group, and we read, " It is said that augite has 

 never yet been found with quartz or orthoclase." " Per- 

 lite" is confounded with " sphaerulite," certain rocks are 

 spoken of as acid/^, trachytes are classified as qiiartzless 

 and quarizose, and no mention is made of the fact that 

 nepheline is a usual and highly important, if not an invari- 

 able, constituent of phonolites. These and many similar 

 errors convince us that Prof. Green has hardly taken that 

 amount of care in mastering those principles of chemis- 

 try, mineralogy, and petrology which are indispensable to 

 the presentation of this part of his subject in a manner 

 that will be of real service to the student. And this conclu- 

 sion is confirmed when we examine the classification of 

 rocks adopted by the author, and many of his definitions, 

 such as those of rhyolite, hypersthene rock, and leucite- 

 rock ; or again, when we mark the want of judgment so 

 frequently shown by him, as, for example, in rejecting the 



name of " porphyrite," while he retains that of " apha- 

 nite." Of the little care that has been taken to bring 

 this part of the work " up to date," we have proofs in 

 the circumstance that the dimorphism of silicic acid is not 

 mentioned, and that leucite is spoken of, without hesita- 

 tion, as belonging to the ctibic system. 



It is only fair, however, to point out that this very great 

 want of accuracy is far more conspicuous in the earlier 

 portions of the book than in its later chapters. This is a 

 most unfortunate circumstance, inasmuch as we fear that 

 many teachers who examine the work with a view to 

 determine its fitness for the wants of students will be 

 tempted to lay it down with feelings of disappointment 

 and despair before they arrive at its really valuable 

 portions. 



We caniK>t but remark that Prof. Green's partial failure 

 in a work which in many respects presents so much of 

 promise, seems to us to have arisen from the attempt, which 

 he boldly avows in his preface, that of making the teaching 

 of physical geology take precedence of that of petrology 

 and palaeontology. While the petrological division of his 

 work is treated so much more feebly, as we have already 

 seen, than the other portions of the subject, the palaeon- 

 tological is omitted altogether. We do not think this can 

 be safely done in any work on physical geology, and the 

 danger of attempting it is well illustrated in Prof. Green's 

 endeavour to explain the manner in which the conditions 

 under which different deposits mu«t^have been" formed is 

 determined by geologists ; in this explanation he almost 

 entirely ignores the important evidence afforded by the 

 characters of the animals or plants ■ embedded in the 

 sediments. 



Rocks and fossils are the objects with which the geolo- 

 gist is called upon to deal at every step of his inquiries, 

 and an accurate, if not an extensive, knowledge of them, 

 is indispensable to the student, before he can hope to 

 grapple successfully with those " broader questions " for 

 which our author shows so much partiality. We cannot but 

 regard the attempt to teach physical geology without the 

 aid of petrology and palaeontology, as bearing a suspicious 

 resemblance to the specious promises which are made 

 by those who profess to be able to impart a know- 

 ledge of a language without instruction in its grammar. 

 We are sure that if such an experiment could have 

 been successful it would have been so in the hands of so 

 experienced a field geologist, so earnest a teacher, and so 

 lucid a writer as Prof. Green ; and, if he has to some 

 extent failed, it is only because a more complete success, 

 under the conditions accepted by him, was impossible. 

 Had our author shown more deference towards the results 

 attained by petrologists, we feel convinced that he would 

 have written with far less boldness on such open ques- 

 tions as that of the "metamorphic origin of granite ; " and 

 had he admitted the importance of palaeontological evi- 

 dence, he would have recognised the difficulties which 

 stand in the way of the acceptance of the theory of alter- 

 nations of universal hot and cold climates during the 

 earth's past history dependent on astronomical causes. 



The views of scenery in the book are admirably 

 selected, but unfortunately their value as illustrations of 

 the text is greatly detracted from by the inferior style 

 in which, in too many cases, the wood-engraving has 

 been executed. 



