408 



SCIENCE 



[N. S. Vol. XXX. No. 769 



for the salary of such a clerk. I understand 

 from Dr. Stiles that $1,200 would pay for the 

 salary of a clerk. I would suggest, therefore, 

 that ten of the leading Museums of the United 

 States pay each $60 toward this expense and 

 that $60 be paid by ten museums of Europe. 

 Those in America to be the "National Museum 

 and those at Cambridge, Boston, New York, 

 Brooklyn, Philadelphia, Pittsburgh, Chicago, 

 Milwaukee, San Francisco. It would, of 

 course, have to be recognized that this charge 

 would be an annual one. 



If the great museums of this country would 

 thus voluntarily pay such a tax, the court of 

 reference for questions of zoological nomen- 

 clature would become permanently estab- 

 lished. 



Chas. B. Davenport 



SCIENTIFIC BOOKS 

 Igneous Bocks. By Joseph P. Iddings. Vol. 

 I., Composition, Texture and Classification. 

 8vo, xi + 464 pages, 130 figures and two col- 

 ored plates. New York, John Wiley & Sons. 

 1909. 



It is not often that a work appears in the 

 literature of any science which stands out so 

 clearly from other corresponding works in re- 

 spect to both its point of view and its intrinsic 

 value that it must be accorded the rank of 

 epoch making. But such is the fact in the 

 writer's opinion concerning the volume by Pro- 

 fessor Iddings which is the subject of this 

 notice. Here is a treatise on igneous rocks 

 which does not in the least pattern after the 

 numerous works on the subject, but from the 

 outset follows a new plan. The author has 

 studied the igneous rock with the aid of mod- 

 ern developments in physics and chemistry 

 and makes the understanding of composition 

 and texture in the light of those developments 

 the all-important thing. 



The point of view of the author may be in a 

 measure inferred from the order in which the 

 properties of igneous rocks are presented, and 

 the manner in which they are discussed in 

 Part I., on Composition and Texture. The 

 igneous rock is, of course, the product of the 

 consolidation of a molten magma. The funda- 

 mental property which the rock shares with 



the magma from which it was derived is its 

 chemical composition. Hence the work pre- 

 sents in Chapters I. and II. the characteristic 

 facts as to the chemical composition of the 

 rocks and of their constituent minerals. 

 Groups of rock analyses are given and a full 

 statement of the various devices used by 

 petrographers to represent in diagrams the 

 significance of the varying amounts of differ- 

 ent components shown by analysis. Two col- 

 ored plates represent many hundred analyses 

 by means of diagrams of Iddings's own design. 



A departure from the usual procedure in 

 discussing the chemical composition of rock 

 minerals is made by taking up the chemical 

 elements known to occur in rocks and, consid- 

 ering them in groups of Mendeleeff's table, 

 indicating the mineral into which they are 

 likely to enter under the associations and re- 

 strictions of the case. 



The fact that an igneous rock is derived 

 from highly complex molten solution by 

 crystallization is to the author abundant rea- 

 son for insisting that the petrographer should 

 understand the principles of physics and 

 chemistry applicable to rock magmas and 

 Chapter III. is devoted to this subject. Special 

 attention is given to the properties of magmas 

 as solutions, and to the chemical reactions 

 which may take place under certain conditions 

 in solutions, expressed in the terms of modern 

 physical chemistry. 



Following this general discussion is one in 

 which the chemical reactions likely to take 

 place in rock magmas under the conditions 

 prevailing in the crustal zone of the earth are 

 particularly considered. Taking the thirteen 

 constituents which are prominent in most 

 igneous rocks the controlling influence of rela- 

 tive chemical activity, strength of combina- 

 tion, affinity of certain elements for each 

 other, and the effect of differing proportions of 

 the elements, are considered in their bearing 

 on the formation of observed rock minerals. 

 To a large extent the reasons for the abundance 

 of certain mineral molecules and the rarity of 

 others containing the same substances are 

 plain. The laws which control the common 

 association of some minerals, the apparently 

 antithetical relations of others, and the de- 



