456 The American Naturalist. 
type reductions of the drawings made by the assistant geologists. 
plates of fossils accompany the chapters of the several format 
These are half-sized reproductions of the figures of fossils given 
Report P. 4, Dictionary of the Fossils of Pennsylvania and the 
rounding States, published in 1889-1890. ; 
The present report has been evidently written with an eye tothe 
general rather than the scientific public. As a popular synopsis of 
the geology of Pennsylvania, it will have much utility. Asad 
sion of the more abstruse problems presented by the structure of 
formations of the State, especially of the eastern region, it has 
value. a 
The Earth’s History,’ by R. D. Roberts, is an attempt “to 
nish a sketch of the methods and chief results of geological eng 
such as a reader interested in the subject for its own sake would ¢ 
- to obtain. It is not intended to be a text-book of Geology.” I 
_ ning with a brief history of geological thought, it takes up the 
history and shows how geologists are enabled to trace the succe 
steps in the development of the earth’s physiography, by reference 
the records of the rocks as interpreted by means of the results of 
tigations into the processes at present active on and beneath its sur 
The central idea of the author is “ to reconstruct, from ancient 
mentary remains, the old conditions that characterized the succe 
stages in the evolution of the land areas; to make out the life 
- of the earth,” and this idea has determined the method of 
the subject matter. The book is not crowded with geological fae 
1s not a dry abridgment of some popular manual of geology, but 
exactly what its author intended it should be—an exposition 
logical logic. Its style is simple and clear, its statements are 
and its various parts are well proportioned. In short, it is an © 
volume for collateral reading for college classes in geology, and 
Introduction to the geological methods for general students.—W. 
_ Wright’s Light,’ although mainly a discussion’ of light 
nomena that may be projected upon the screen by means of a 
: with the lime light, is nevertheless, an excellent volume for § 
___*The Earth’s History, an Introduction to Modern Geology, by R- D. 
A Pri 4 Apren fan ~ York: Scribner's Sons, 1893, pp- 
ae ‘Light, nt, a course of Experimental Optics, chiefly with the Lantern. 
_ Wright; 2d Ed, Macmillan & Co., pp. 301, PI. 9, Figs. 207. Price, $3: 
