We ORE 
avers os 
THURSDAY, APRIL 23, 
1914. 
A TREATISE ON .IGNEOUS ROCKS. 
Igneous Rocks. Composition, Texture and 
Classification, Description and Occurrence. By 
Joseph P. Iddings. In Two Volumes. Vol. i. 
Pp. xi+464+3 plates. (1909.) Price 21s. net. 
Vol. ii. Pp. ix+685. (London: John Wiley 
and Sons, Inc.; London: Chapman and. Hall, 
Ltd., 1973:)* Price 25s. 6d. nets 
NIFORM with the ‘Rock Minerals” of the 
same author, now in its second edition, the 
work which Prof. Iddings has now completed will 
take an assured place as the fullest and most 
comprehensive treatment of the subject in our 
language. Nor is it of the nature of a com- 
pilation, but presents numerous features of origin- 
ality. There are novelties which will be cordially 
welcomed, and others which will probably meet 
a more doubtful reception. The author has not 
shrunk from introducing many debatable ques- 
tions, and has pronounced on them in no un- 
certain tone. Although the spirit is that of the 
missionary rather than the controversialist, this 
somewhat impairs the utility of the work as a 
hand-book for students. 
The first volume, which has been for some time 
in the hands of petrologists, deals with the com- 
position, texture, and classification of igneous 
rocks. It includes a good account of the 
chemical composition of the rocks and of their 
component minerals, a discussion of the chemistry 
and physics of rock-magmas, an admirable and 
well-illustrated chapter on rock-textures, and a 
statement of the problem of magmatic differentia- 
tion. The last three chapters are concerned with 
the thorny subject of nomenclature and classifica- 
tion. Here we have first a historical sketch, then 
an arrangement of the principal igneous rocks in 
~a “qualitative ” mineralogical scheme, and finally 
an exposition of the ‘‘ Quantitative Classification,” 
of which our author is one of the creators. _ 
The second volume, recently issued, deals with 
the description and occurrence of the rocks, and 
is divided into two equal parts. The final test of 
any classificatory scheme is its applicability in | 
practice; and doubtless many petrologists have | 
waited with curiosity to see how the author would 
develop a systematic treatment of igneous rocks 
on the lines of the Quantitative Classification. 
seems that we may now congratulate him on 
recognising the impossibility of the task, for the 
system actually adopted does not differ in general 
plan from others in current use. The rocks are 
first divided into those characterised by (1) pre- 
NOs.@321, VOL. .93} 
It | 
ponderance of quartz, (2) quartz and _ felspar, 
(3) felspar, (4) felspar and felspathoids, (5) fels- 
pathoids, and (6) ferro-magnesian minerals. Under 
each head ‘“phanerites” and “aphanites” are 
separated, while the subdivisions are again based 
on mineralogical characters. To introduce the 
| quantitative element, the author has often re- 
defined terms already in use (a practice which he 
deprecates in others); but he has succeeded in 
producing a working scheme with less disturbance 
of accepted usage than-we had expected. The 
principal relic of the specific ‘‘ Quantitative Classi- 
fication”? is the use of an ideal mineral composi- 
tion (the “norm ’’) instead of the actual composi- 
tion. 
Nevertheless, there are many signs that the 
author is reluctant to abandon the conception of 
a Classification laid down a priori. The precise 
boundaries which he demands are to be fixed by 
arithmetic, not by chemistry. He counts it a 
defect of the current systems that special import- 
ance is attached to the presence of even very small 
amounts of certain minerals, such as nepheline 
and leucite; but, as he has himself pointed out 
(prior to the birth of the Quantitative Classifica- 
tion), the mere appearance of one of these minerals 
shows that we have crossed a significant boundary- 
line in respect of chemical composition. Surely it 
is he, not his critic, who has lost appreciation of 
“the mathematical precision of stochiometric 
chemistry ” (p. 7). 
The second part of the volume we can praise 
without reserve. It is an account, such as has 
never been attempted before, of the geographical 
distribution of igneous rocks over the globe, with 
special reference to their chemical composition. 
This has not been merely compiled in the library, 
but represents the results of much travel and study 
in many lands. It is illustrated by maps of the 
several continents, and by more than 1200 
analyses. We hope that in another edition some 
attempt will be made to distinguish on the maps 
igneous rocks of different. geological ages. 
AG Ea 
MATHEMATICS FOR FRENCH 
FRESHMEN. 
Les Principes de l’Analyse Mathématique: Exposé 
Historique et Critique. By Prof. P. Boutroux. 
Tome Premier. Pp. xi+547. (Paris: A. Her- 
mann et Fils, 1914.) Price 14 francs. 
ROF. BOUTROUX appears to belong to 
the school of the laughing philosophers ; 
for, like many of his distinguished compatriots, 
he has composed a work which is amusing as well 
I 
