150 The American Naturalist. [February) 
RECENT LITERATURE. 
Zirkel’s New Text Book of Petrography.'—Although entitled 
a‘ Lehrbuch’ the revision of Prof. Zirkel’s well known Petrography 
has rather the character of a‘ Handbuch.’ The first of the three 
volumes proposed to complete the work contains an introduction to 
the study of rocks, a description of the methods made use of in this 
study, an account of the peculiarities of form presented by rock-form- 
ing minerals, a review of the characteristics of each of the most 
important of these, a discussion of rock structure and the causes of its 
variation, a statement of the method of occurrence of rock masses, 
a chapter in the physical properties of rocks and one on the changes 
_ which they undergo when subjected to external influences. Following 
these, which occupy in all 635 closely printed pages, there are sume 
190 pages in the mineral, chemical and structural relations of massive 
rocks, and a very full discussion of the theories proposed to explain 
the origin of the variations observed in rock masses, and in the differ- 
ent emanations from the same volcanic centre, which concludes with 
the scheme of classification for massive rocks that the author intends 
to follow in the succeeding volume. 
As the synopsis of the contents shows Prof. Zirkel expects to cover 
the entire field of petrography in a way that has never been attempted 
hitherto. He will treat not only of the massive rocks, but of the sed- 
iments and crystalline schists as well. The first volume gives n0 ee 
dence as to the fullness with which the individual rock types will, 
discussed, but it is quite certain that the three volumes will fill a place 
that has long been ready for them in the working room of every Pf 
trographer. 
The special excellencies of the volume before us consist in tha ies 
complete bibliographies appended to or inserted within the paragrap" 
pertaining to different heads, the thoroughness with which the: a 
has been covered by it, and the freshness of the material been R 
covers. Of course the second edition is not a revision of the aut pea 
first edition of the Lehrbuch, It is an entirely new book, pede?’ 
from ‘ preface to finis.? And more than this—it contains referent n i 
the very latest petrographical researches published in this coun ge x 
*Lehibuch der Petrographie by Dr. Ferdinand Zirkel. 2te Aufl., Erster Bunt 
Leipzig, Wilhelm Engelmann, 1893. Pp. x and 845. 
