Part I: Physical Geology. 425 
sprang up on the discovery of some sensational and mysterious crime. 
The increase in the power and range of the modern laboratory has, 
however, enabled many crucial problems to be isolated and studied in 
careful detail, and much real progress hasbeen made. The application 
of the principles of physical chemistry has thrown an illuminating 
light upon the question of the mode of formation of both igneous and 
sedimentary rocks. Thus, van t’ Hoff and his school have, by their 
classical researches, cleared up the difficulties that at one time puzzled 
the student of salt deposits, and the important series of investigations 
which have for some years past been carried out at the Geophysical 
Laboratory of Washington upon the conditions under which some of 
the important and refractory mineral constituents of rocks crystallize 
out are gradually unravelling the tangled problem presented by the 
igneous rocks. So much has been accomplished that a new textbook 
by one who has been so closely in touch with the trend of modern 
investigations is heartily welcome, and this volume is one which we 
can thoroughly recommend, not only to the student, but also to the 
general reader. The author, following a custom which has been 
extensively followed in recent American textbooks, makes skilful use 
of two sizes of type, the larger for the more general and important 
statements, and the smaller for additional or subsidiary detail. 
We must not omit a note of praise for the numerous excellent 
illustrations which considerably enhance the value and interest of 
the book. : 
Part i of the complete textbook comprises two main divisions: 
I, Dynamical Geology, and II, Structural Geology. The former, 
which, as its title indicates, deals with all that has played a part in 
fashioning the crust of the earth into the form in which we know it 
to-day, is subdivided into ninechapters. The first is devoted to the 
atmosphere and its work, and the second to the closely allied subject 
of rain and running water; the air has powerful mechanical and 
-chemical action, and the water precipitated from it produces rivers, 
which carving out paths for themselves bear material to the oceans. 
In the third chapter we read of lakes and interior drainage, and in 
the fourth of the ocean and its work; as a geological factor the sea 
acts in much the same way as inland waters, but, of course, on 
a very much bigger scale, the agencies being currents, tides, and 
waves. An extremely interesting chapter follows on ice as a geological 
agent. The contrast between the eroding effect of ordinary 
weathering and running water and that of glaciation is well shown 
by three excellent sketches. The final four chapters treat successively 
ef underground water, organic life and its geological work, igneous 
agencies, and lastly movements of the earth’s shell. To human 
perceptions volcanoes and earthquakes are cataclysmal events, but 
considered from the geological point of view they are not so important 
as many other far less awe-inspiring agencies. 
The second division, on Structural Geology, which is a little shorter 
than the first, opens with an introductory chapter on the general 
structure and properties of the earth. In the discussion of rocks and 
ore deposits which fills the rest of this division Professor Pirsson not 
only does not use, but does not even refer to, the ambitious chemical 
