202 
SOME RECENT WORKS ON PETROLOGY AND MINERALOGY. 
Principles of Chemical Geology, by J. V. Elsden; pp. vili.+222 ; 
London: Whittaker & Co., Igto. 
Igneous Rocks, vol. i., by J. P. Iddings; pp. xi.+464; New York: 
Wiley & Sons, 1909. 
An Introduction to Petrology, by F. P. Mennell ; 2nd edition, pp. vii. +- 
204; London: Gerrards, Limited, 19ro. 
The Recognition of Minerals, by C. G. Moor; pp. vii.+231; Mining 
Journal, no date. 
It is very generally recognised that the comparatively new science of 
Physical Chemistry has many and important applications to the problems 
of Geology, and especially of Petrology. That no very great progress has. 
yet been made on these lines is due to the inherent complexity of the 
operations of Nature as compared with those of the laboratory, but partly 
also to another cause. The chemist has not, as a rule, sufficient acquaint- 
ance with geological questions to apply his know ledge ; while the geolog- 
ist is seldom well versed in a special branch of chemistry w hich is of 
recent and rapid growth. We are the more indebted to Dr. Elsden, who, 
combining both qualifications, has given in the volume before us the 
desired connecting link. According to the sub-title of the book, it is 
‘a review of the application of the Equilibrium Theory to Geological 
Problems.’ In successive chapters he considers equilibrium in reference 
to fusion, viscosity, diffusion, surface-tension, vapour-pressure, poly- 
morphism, solution, eutectics, and solid solution. Each chapter is full 
of useful matter, and furnished with copious references. If we have any 
criticism to make, it is that, in the effort to compress so much into a small 
compass, the treatment becomes in some places rather fragmentary and 
tantalizing. Nevertheless, the book will be heartily welcomed by the 
student. 
Professor Iddings’ volume, uniform with his * Rock Minerals’ (1906), 
must rank as the best and fullest account of the characters of igneous 
rocks hitherto offered to the English reader. The earlier chapters deal 
with the chemistry of the subject. Chapter I. gives a very clear and useful 
view of the chemical composition of igneous rocks, with a comparison of 
various devices for the graphical presentation of rock-analyses. Chapter 
II., which treats of the chemical composition of the constituent minerals, 
might perhaps be abridged with advantage, and more space given to the 
important chapters which follow: viz., those devoted to the chemistry 
and physics of rock-magmas in the light of accepted principles. Of special 
value is Chapter VI., on the textures of i igneous rocks, illustrated by numer- 
ous well-chosen figures, Next comes a discussion of magmatic differentia- 
tion, which will be read with interest. Then, after a rather brief account 
of the modes of occurrence of igneous rocks, we come to the second part 
of the book, dealing with classification and nomenclature. This consists 
of three chapters. The first is a historical review; the second groups 
the more important igneous rocks in a ‘ qualitative ' mineralogical system ; 
and the third is an exposition of the ‘ Quantitative Classification,’ of which 
the author is joimt-creator. Concerning the value of this, we have our 
own opinion, which cannot be set forth in this place. Suffice it to say 
that we shall await with lively curiosity the appearance of volume II., 
in which the author must face the task of a systematic account of igneous 
rocks in terms of the new classification. 
The student of petrology has the choice of numerous text-books which 
have appeared in Germany, France, and England. Mr. Mennell’s book 
is written from Bulawayo, and many of the illustrations are drawn from 
South African sources. Beginning with the collection of specimens and 
the preparation of thin slices, the author goes on to give a concise account 
of the characters of crystallized minerals. The crystallographic part is 
too brief to be of much service ; but the use of optical properties in dis- 
criminating the common rock-forming minerals is clearly set forth, and 
Naturalist, 
