REVIEWS 679 
water faunas to intermingle to a considerable extent after the time repre- 
sented approximately by the Topeka limestone, unless by a circuitous 
route, no one acquainted with the geology of the intervening region would 
hesitate to state. 
It is very difficult to determine what Dr. Girty’s conclusion as to the 
relative age of the Guadalupian, Russian, and Kansan deposits is. It is 
very evident, however, from the bulk of his reasoning, that he considers 
both of the former younger than the Kansan deposits. It is also to be 
remembered that the book was written, and perhaps in type, before the 
later Kansas studies were published. He was also handicapped by the 
fact that he was without a personal field knowledge of the Kansas Permian 
deposits, and for this reason fails fully to appreciate the changed aspect of 
the fauna, noted by all the paleontologists who have studied the region, 
from Meek to Prosser. J. W. Breve 
A Key for the Determination of Rock-jorming Minerals in Thin 
Sections. By ALBERT JOHANNSEN, PH.D. New. York: John 
Wiley & Sons. 
This work contains about 540 pages of text and tables conveniently 
arranged for laboratory use. It is much more than a key, for all of the 
most useful optical methods are described in a concise manner, which 
will be appreciated by anyone who is engaged in the microscopic study of 
rock sections. It will be especially helpful to the geologist who uses 
petrology as an aid to the study of problems of general or economic geology 
and who finds it necessary to review his optics each year at the beginning of 
the period of office work. 
The arrangement of the tables is original and excellent. The first page 
of the table for each group is a diagram showing the birefringence, double 
refraction, and optical character of each numeral of the group. The color 
plate or table of birefringences in the back of the book is large enough to be 
useful and not too large to be handled conveniently. There is hardly a 
diagram ora table which is used by petrographers in everyday practice 
which is not given in the Key and the whole arrangement is designed to 
gain accuracy and save time. We JEL 18 
Synopsis of Mineral Characters. By RatpH W. RicHarps. New 
York: John Wiley & Sons. 
In this useful work of 100 pages the most important minerals are 
arranged alphabetically and their chief chemical and physical character- 
