276 Reviews — Dr. F. H. Hatches Petrology. 



E, E "V I E "W s. 



I. — An Introduction to the Study of Petrology: the Igneous 

 EocKS. By Frederick H. Hatch, Ph.D., F.G.S. pp. 128. 

 (London, Swan Sonnensclaein & Co. 1891.) 



THE object of this little book (as stated in the preface) is to 

 describe the mineral constituents and structure of the Igneous 

 Eocks, their mode of occurrence and origin ; and the author has 

 fulfilled his task in an accurate, clear, and concise manner. 



Petrology is rapidly developing a language of its own, and 

 Dr. Hatch, who has already done good service in explaining the 

 meaning of its many terms in his Glossary (appended to Teall's 

 British Petrography), gives also many useful definitions in his 

 present work. It will be of service, therefore, as a text-book for 

 students who are giving especial attention to Igneous rocks, while 

 to geologists in general it will be a handy book of reference on the 

 principal Igneous rocks, and their distribution in the British Islands. 

 These portions of the subject occupy about one-half of the volume, 

 the other half being mainly devoted to the constituent minerals. 

 We may observe, by the way, that a few diagrams showing the 

 mode of occurrence of the rocks would have been useful. 



The title of the book is, perhaps, a little misleading (unless the 

 ■work be intended to form one of a series), for the author has 

 brought us into the presence of Petrology, without giving us any 

 real introduction. The student will find that he cannot make 

 acquaintance with the subject without a good preliminary know- 

 ledge of Optics and Crystallography, to say nothing of Chemistry. 

 Dr. Hatch, it is true, states that the scope of his work is too small 

 to admit the treatment of Optical phenomena, and he refers the 

 student to the lately published and excellent '• Notes on a New 

 Form of Polarizing Microscope," by Allan B. Dick. Mr. Dick's 

 "beginner" is told how to measure angles of extinction, and how 

 to observe the " dispersion," and the character of the pleochroism of 

 any mineral, but even he must start with some preliminary training, 

 and Mr. Dick recommends Spottiswoode on Polarized Light. 



Thus the student who wishes to master the methods of research, 

 and be enabled to undertake investigations on his own account, 

 must seek help elsewhere. He will find much practical information 

 in Eutley's " Rock-Forming Minerals," but that work is not altogether 

 free from technical terms, that may be familiar to the advanced 

 student, but which might discourage the beginner. Prof. Cole's 

 "Aids in Practical Geology" introduce the subject in a far simpler 

 form, and thus provide more easy lessons on Petrology and its 

 methods of research. Dr. Hatch's book contains only the main 

 facts concerning Igneous rocks, and it will not educate the student 

 to identify his specimens. 



Although the identification of Igneous rocks is a task that now- 

 a-days requires much special training, Petrologists unfortunately 

 appear to attach but little importance to rock names. They prefer 



