32 



SCIENCE 



[N. S. Vol. XXIX. No. 731 



SCIENTIFIC BOOKS 

 A Key for the Determination of Rock-forming 

 Minerals in Thin Sections. By Albert 

 JoHANNSEN. New York, John "Wiley & 

 Sons. 1908. 



This key has been prepared, as the author 

 states, for the reason that tables for the optical 

 determination of minerals in thin sections 

 have heretofore been made of secondary im- 

 portance in test-books. Most of the books on 

 this subject, while admirable in their way, 

 are of more use to trained mineralogists than 

 to beginners, this being due principally to the 

 absence of " classification." 



The book is divided into four parts : Part 

 I. treats of introductory optics, measurements 

 to be made with the microscope and the 

 methods of recognizing the common optical 

 characters of minerals. Part II. takes up the 

 general discussion of the relations between the 

 different members of the common groups of 

 minerals. Diagrams are here given to assist 

 in the determination of the species in the 

 pyroxene, amphibole and feldspar groups. 

 The part treating of the feldspars is par- 

 ticularly elaborate, giving fourteen methods 

 of investigation. Part III. (415 pages) gives 

 an explanation of the tables and contains a 

 very elaborate scheme for determination, 

 based on a systematic identification of the 

 fundamental optical characters of the min- 

 erals in question, the minerals with similar 

 optical characters being grouped in the same 

 part of the scheme. Following the descrip- 

 tion of each mineral are given the distinctions 

 between it and other similar minerals. Part 

 IV. contains tables of mean indices of re- 

 fraction, maximum birefringences, specific 

 gravities, and also lists of minerals by crystal- 

 line system and "habit." A summary is ap- 

 pended of the optical characters of the 

 minerals in alphabetical arrangement, which 

 is very convenient, as it does away with the 

 necessity of remembering the author's special 

 arrangement, a universal fault to be found 

 with other tables. 



This book represents a very elaborate and 

 painstaking collation of the important optical 

 and crystalline characters of some one hun- 



dred and sixty-four rock-forming minerals, 

 and, for the first time in the literature of the 

 subject, the minerals have been arranged in a 

 way for systematic optical determination. A 

 further advantage lies in the fact that these 

 optical and crystalline characters are always 

 recorded in the same order and that para- 

 graphing is freely used. The author has 

 made the introductory discussions on optics 

 and determination of optical characters as 

 simple as possible, but has given detailed foot- 

 notes referring to more complete theoretical 

 discussions of the underlying principles. 

 Standard authorities have been consulted in 

 the preparation of the general data, but the 

 tables might have proved more useful had 

 authorities been cited. 



The scope of the work along optical lines is 

 similar to that covered by Penfield and Brush 

 in their " Tables for Blowpipe Determination 

 of Minerals." 



The scheme is sufficiently elastic to provide 

 for mistakes likely to be made in the determi- 

 nation of some of the optical characters, as 

 for example, extinction angles. Minerals 

 with small extinction angles (under 5°) are 

 found in two places of the scheme, both with 

 minerals with inclined extinction and with 

 those with parallel extinction. The micro-pho- 

 tographic cuts of interference figures are very 

 good and many of the tests are explained with 

 the aid of detailed diagrams, so that they may 

 be easily and quickly made. A good color 

 chart of the interference colors (after Levy 

 and Lacroix) is appended. 



The value of the book might have been in- 

 creased by a more detailed description of the 

 types of petrographical microscopes and their 

 common adjustments. Also the suggested in- 

 denting of the pages of the text is a matter 

 of much trouble and an arrangement provid- 

 ing for this being done by the printer would 

 certainly prove of great advantage in subse- 

 quent editions. 



L. McI. L. 



Southern Agriculture. By P. S. Eaele. Pp. 

 vi + 29Y. Containing 9 half-tone plates, 

 many text cuts, and full index. New York, 

 The MacmiUan Co. 1908. 



