374 



SCIENCE 



[N. S. Vol. XXVni. No. 716 



less than a wanton massacre of the innocents. 

 And the helplessness of the individual, even 

 ■when attended by the best of medical prac- 

 titioners, in contending alone with the general 

 conditions which play havoc with the health 

 of the most favored people, has convinced 

 every one of knowledge and sense that the 

 maintenance of the public health is a public 

 function. As there is a community of in- 

 terests at the bottom of the health question, so 

 there must be community of effort. — The 

 Springfield Republican. 



SCIENTIFIC BOOKS 

 Rocks and Roch Minerals. A Manual of the 



Elements of Petrology without the Use of 



the Microscope. By Louis V. PmssoN. 



New York, John Wiley and Sons; London, 



Chapman and Hall. 12mo. Pp. 414, 74 



£gs., 36 plates. 



Few if any petrologists are better qualified 

 by reason of notable attainments in the 

 science, as well as by long experience in 

 teaching it, to write a manual of petrology 

 than is Professor Pirsson, of Tale University, 

 and it is with pleasure that we note the ap- 

 pearance of the book before us. Teachers of 

 petrology will in general, we believe, fully 

 agree with the author's opinion, as expressed 

 in his preface, that there has long been a 

 need for a " small, concise and practical 

 treatise" on petrology in which the subject 

 is dealt with entirely from a megascopic 

 standpoint. Mining engineers and others 

 who have to deal with rocks in a practical 

 way have also felt the urgent need of such a 

 book for purposes of reference. In our opin- 

 ion the present manual meets this need in a 

 highly satisfactory manner, and its publica- 

 tion marks a distinct advance in the treat- 

 ment of elementary petrology. A general 

 idea of the scope of the book may be obtained 

 from the table of contents which follows : 



Part L, Introductory and General Consid- 

 erations. Chapter I., Scope of Petrology: 

 Historical Methods of Study; Chapter II., 

 Chemical Character of the Earth's Crust and 

 its Component Minerals. 



Part II., Eock Minerals. Chapter TTT , 

 Important Properties of Minerals; Chapter 

 IV., Description of the Eock-making Min- 

 erals; Chapter V., Determination of the 

 Eock-making Minerals. 



Part III., The Eocks. Chapter VI., General 

 Petrology of Igneous Eocks; Chapter VII., 

 Description of Igneous Eocks ; Chapter VIII., 

 Origin and Classification of Stratified Eocks; 

 Chapter IX., Description of Stratified Eocks; 

 Chapter X, Origin, General Characters and 

 Classification of the Metamorphic Eocks; 

 Chapter XL, Description of the Metamorphic 

 Eocks; Chapter XII., The Determination of 

 Eocks; Index. 



The arrangement of the material in the 

 various chapters is admirable throughout, 

 while discussions, descriptions and state- 

 ments in general are accurate, clear, concise, 

 yet sufficiently complete, and are written in a 

 style which is attractive and easy to read. 

 Chapter IV., dealing with the general petrol- 

 ogy of the igneous rocks, seems particularly 

 worthy of notice, since it presents such ma- 

 terial of a general character, both practical 

 and theoretical, as is really essential for a 

 clear understanding of igneous rocks, in a 

 manner entirely in keeping with the most 

 recent developments of the science, and yet 

 within the comprehension of those not 

 thoroughly trained in physical chemistry, nor 

 in micro-petrology, a task that is not an easy 

 one. An idea of the contents of this chapter 

 may be gathered from the following topics, 

 which are among those discussed therein: 

 The modes of occurrence of igneous rocks; 

 the chemical composition of magmas and their 

 differentiation; the crystallization of silicate 

 solutions (magmas) and the development of 

 texture in igneous rocks; contact metamor- 

 phism; the classification of the igneous rocks. 



In regard to the classification mentioned 

 above, a system has been developed entirely 

 consistent with megascopic petrology, all 

 distinctions being based upon differences of 

 texture or of mineral composition that can be 

 made out by the careful study of good hand- 

 specimens with the aid of a pocket lens, and 

 a knife, in some few instances supplemented 



