188 The American Geologist March, 1890 
history studies. It treats especially of the morphology of organisms, but 
almost entirely of extinct forms. Hence it is of particular interest to 
the paleontologist. It is also of service to the evolutionist, since extinct 
forms are of most service in demonstrating the laws of phylogeny. 
The work may be divided into two parts, — the first treating particu- 
larly of the geological, and the second of the biological phases of the 
subject. The opening chapter deals with the scope and importance of 
the history of organisms. Chapter II, which treats of the making of 
the geological time scale, is of much interest to both geologist and pale- 
ontologist. This subject is treated historically, and the development of 
our present time scale is discussed at some length. The following chap- 
ter treats of the divisions of the time scale and of their time values. The 
several geological revolutions are briefly stated and their relations to the 
major divisions of the time scale pointed out. Then follows a discussion 
of the comparative lengths of the several divisions of the time scale and 
the methods of computing these. Chapter IV treats of the stratified 
rocks, and chapter V of fossils and their geological range. The next two 
chapters relate to the geographical distribution of organisms and of their 
relation and adjustment to environment. 
With chapter VIII begin the strictly biological phases of the work. 
The nature of species is first discussed. Ideas of various naturalists as 
to what constitutes a species are stated, and the nature of the mutable 
and immutable schools discussed. "What is an organism?" is considered 
in chapter X, which also contains a brief statement of the principles of 
embryology. In the chapter on the origin of species the views of Dar- 
win and Cope are stated as illustrating the nature of the problem and 
also the different views held by naturalists as to the cause of the phe- 
nomena of evolution. The decision is reached by our author that the 
origin of species is still an open question. The age of the various char- 
acters of organisms is also discussed in this chapter, and it is shown that 
this varies greatly. Thus in the brachiopod Spirifera logani Hall the 
class characters extend from the beginning of the Cambrian to the pres- 
ent time, while the specific characters extend over a portion of Eo Car- 
boniferous time only. 
Chapter XI opens with a discussion of the nomenclature used in clas- 
sification. The ideas of Aristotle, Linne, Cuvier and others are stated, 
and it is shown that in tracing out the history of organisms species and 
genera are of most service. This chapter contains also a brief statement 
as to the methods by which the history of organisms may be studied. 
These methods are two: (1) the zoological method depending largely 
upon embryology, and (2) the paleontological method depending upon 
fossils. While these two plans are diverse, it is claimed that their re- 
sults in the main agree. This chapter further contains an instructive 
discussion as to the differentiation among organisms that existed in 
Cambrian time. This differentiation is shown to have been very great 
and was "present at the beginning of the records." With the exception 
of the vertebrates all the grand types of organisms lived in these early 
Cambrian seas, but "So far as these grander differences of organization 
