Reviews—Description of Arthur's Seat Voleano. 525 
Description of ARTHUR’S Seat Votcano. By B.N. Peacn, LL.D., 
F.R.S. Second Edition. Mem. Geol. Survey of Scotland. 
pp. 26, with a coloured map and 4 figures. 1921. Price 2s. 6d. net. 
Jpiane first edition of this admirable little memoir was published 
in 1911. It wasa reprint, with slight changes, of the description 
of the area in the second edition of The Geology of the Neighbourhood 
of Edinburgh. In this second edition Dr. Flett has made a few 
unimportant alterations in the text, and has added another valuable 
feature in an appendix describing the characters and classification 
of the volcanic rocks, according to the modern nomenclature of the 
Scottish Carboniferous petrographical provinee. 
Tur Economic Aspects oF Grotogy. By C. K. Lerra. 
pp. xiii + 457. New-York: Henry Holt & Co. 1921. 
Ope of the most noteworthy developments of recent years in 
scientific thought is the general recognition of the fact that all 
science has an actual or potential economic value. The old lines 
of demarcation between “ pure” and “ applied” science are being 
rapidly swept away, and in no field is this more true than in geology. 
There is, in point of fact, no such thing as economic geology. What 
is ordinarily meant by this term is the special application of geological 
law and theory to problems of present practical moment. During 
the last seven years this has become abundantly manifest, and an 
enormous amount of additional interest has been imparted to our 
science by the realization of its importance as a factor in world- 
politics and world-industry. There is scarcely a single field of 
human endeavour in which geology has not some part; mineral 
resources are, in fact, the foundation of a great part of trade and 
industry, and their political influence cannot he over-estimated. 
Another fact now generally recognized is the economic value of 
purely theoretical investigations. It is unnecessary to labour this 
point ; it must suffice to say that though it is impossible to foresee 
exactly when a theoretical investigation will become of technical 
value, it always does so sooner or later. As an example of this we 
will only mention the bearing of theories of magmatic differentiation 
on the origin of ore-deposits and their discovery and exploitation 
on a commercial scale. 
Such are the ideas that Professor Leith has set himself to develop 
in this book and well has he performed his task. It is shown that 
all branches of geology, even the most apparently abstract, have 
served or may serve some useful purpose. The first 300 pages are 
occupied by a systematic account of the occurrence and distribution 
of mineral deposits, each discussed under two headings, geological 
and economic. The geological sections are necessarily brief and 
somewhat sketchy ; the economic sections describe the distribution, 
output, and applications of the minerals and the principal facts 
