REVIEWS. 
Elemente der Gesteinslehre. By H. ROSENBUSCH, Stuttgart, 1898. 
That this book presents the essential features of Professor Rosen- 
busch’s lectures on petrology as they have been developed during 
thirty years of his experience, is sufficient guarantee that the work is a 
most valuable contribution to the didactic side of the subject. That 
those who are not permitted to listen to Professor Rosenbusch in 
Heidelberg may read his careful presentation of the essential character- 
istics of rocks is fortunate, and the appearance of the book so long 
looked for is a fact upon which many may congratulate themselves. 
No satisfactory review of a work so full of matter can be given with- 
out close and exhaustive reading, but some insight into its character 
may be gotten without exhausting the subject. 
In attempting to condense the wide range of facts and speculations 
relating to igneous, sedimentary and metamorphosed rocks into the 
space of an elementary text-book, minor details and qualifications of 
statements are minimized or omitted, thereby sharpening the out- 
lines of the images presented to the mind. Asa necessary result we 
find in some cases positive statements where we should expect tentative 
ones, and a tone of finality in portions of the work where we had not 
expected it. This is of course noticeable in the introductory portions 
of the parts devoted to the three categories of rocks. 
The general introductory chapter, after defining a rock, and the 
scope of petrology, treats of the methods of investigating rocks, 
geologically, mineralogically and chemically, special attention being 
given to the chemical characteristics. Definitions of the principal 
terms used in connection with the mineral constituents are followed 
by an account of varieties of parting and jointing of rocks and a brief 
statement of their formation and classification. 
Part I deals with eruptive rocks, first considering their constituents 
as chemical compounds and as minerals, and the relation of the latter 
to one another both as to the order of their crystallization and as to 
their morphology. Then their geological characteristics are described. 
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