46 
REVIEWS. 
Feb.. 1891. 
not materially contribute to a settlement of the problem of the method 
of evolution, but at the same time it is distinctly useful as collecting 
into a small space the principal objections which have been raised 
against the greatest theory yet enunciated to explain the origin of 
species. The printing is clear, and the index excellent. 
A. B. B. 
An Introduction to the Study of Petrology : The Igneous Rocks. Intro¬ 
ductory Science Text-Books. By F. H. Hatch, Ph. D., F.G. S. 
London : Swan, Sonnenschein and Co. 
Although there are several works in English which treat fully of the 
Petrology of Igneous Rocks, yet there is none which is sufficiently 
elementary, and at the same time full and accurate enough, to supply 
all the needs of the beginner in the subject. This gap in scientific liter¬ 
ature, Dr. Hatch, so well known for his writings on Petrology, has now 
adequately filled, for he has produced a book which will be in the 
hands of all students and teachers of the subject, both because there 
is no work of just the same kind in English, and because of its 
admirable character. 
In the preparation of this book, the author has freely made use of 
the works of Yon Lasaulx, Rosenbusch, Fouque, Levy, Lacroix, and 
Teall; the illustrations are drawn from these and other sources. 
These names and that of the author are sufficient guarantee of the 
accuracy of the statements made in this little work, which presumes 
the reader to possess a certain amount of knowledge of optics and 
crystallography, but in other respects is elementary in nature, while at 
the same time it contains the results of the latest and most advanced 
investigations. 
The plan of the book is as follows :—First, we have an account of 
the occurrence of the igneous rocks ; then, their constituent minerals 
are described. Following these chapters comes one on the structure, 
chemical composition, and alteration of the igneous rocks, preliminary 
to a classification and description of the same, which latter subjects 
take up more than a third of the book. In classifying the igneous 
rocks, a very difficult task, the author divides them into groups 
dependent on the proportion of silica present: then each main group 
is sub-divided into families according to the mode of origin or 
occurrence, while “ mineralogical composition is, on account of its 
extreme variability, allowed to play only a subsidiary role.” 
Two very useful features of the book are : first, the notices of the 
introduction of the respective petrological names, and, secondly, an 
account of the geographical distribution in the British Isles of the 
principal rocks described. The illustrations are in many cases very 
good, and sure to be of use to the student; the printing is clear, and 
the index full and accurate. 
In conclusion, we must congratulate Dr. Hatch on having produced 
a work which will be welcomed by every student of geology. 
A. B. B. 
