374 General Notes. [April, 
MINERALOGY AND PETROGRAPHY.' 
Hussak’s “ DETERMINATION OF ROCK-FORMING MINERALS.”"— 
The appearance in English of any book which treats of the 
methods of the new geology, is a subject for congratulation on 
the part of those who believe that the use of the microscope will 
globe and to the changes which these rocks undergo under vari- 
ous conditions, It is a lamentable fact that, though so much is 
now being done in this field, but few good English text-books 
exist. The only works relating to this subject which have 
appeared in English are Zirkel’s Microscopical Petrography? 
and Rutley’s Study of Rocks. Both of these treat more par- 
ticularly of the classification of rocks and presuppose a know- 
ledge of the elementary principles, by means of which their 
mineral constituents are recognized. It is with pleasure that we 
now welcome a third volume, which treats of the optical proper- 
ties of minerals and the methods which are made use of in their 
detection. Dr. E. G. Smith, of Beloit, Wisconsin, has very re- 
- 85): 
-and one (Kolben) is not translated at all. Certain sections 0 
_ orthorhombic minerals are spoken of as not extinguishing “ for 
_ the most part according to their axial figures” (Figurenaxen) (p. 
23). More serious than these are the errors which arise from the 
confusion of the optical axes with the axes of elasticity; of 
biaxial minerals with those which are doubly refracting; and 
finally of isotropic substances with those exhibiting parallel €x- 
_ tinction. The second part is taken up with a tabular arrangement 
_ of the principal minerals which enter into the composition of ‘ 
1 Edited by W. S. BAYLEY, Johns Hopkins University, Baltimore, Md. 
2 Washington, 1876, 
3 London, 1879. 
* New York: John Wiley & Sons, 1886. 
