358 Scientific Intelligence. 



16. Igneous Hocks and their Origin; by R. A. Daly. Pp. 

 563, 8° '; 205 figs. New York, 1914 (McGraw Hill Book Co.).— 

 This work contains in somewhat changed and revised form the 

 matter published by the author in previous years on various 

 phases of petrology and igneous geology, such as the mechanics 

 of igneous intrusion, the secondary origin of certain granites, 

 classification of igneous intrusive bodies, origin of the alkaline 

 rocks, average composition of rock types, origin of augite ande- 

 sites, differentiation by gravitative adjustment, abyssal igneous 

 injection, etc., together with the theoretical portion of the report 

 on the Geology of the North American Cordillera at the Forty- 

 Ninth Parallel. To this material, which contains the views of 

 Professor Daly on various problems which igneous rocks present, 

 and with which penologists are familiar, much new matter has 

 been added and the whole worked over to present in consistent 

 and systematic manner a treatise upon the origin, emplacement, 

 classification, and other varied relations of igneous rocks. It 

 would be impossible in the limits which necessity imposes on this 

 notice to present an adequate review of the work, but an idea of 

 the mode of treatment of the subject may be gained by a state- 

 ment of the chapter headings and the matter included in them. 

 The author begins with a brief discussion of classification and 

 the reasons for adopting the system of Rosenbusch, according to 

 which the rocks are grouped into genetic clans. Then follows a 

 study of the general distribution and relative quantities of the 

 igneous rock species, and as a general result the writer finds that 

 quantitatively the rocks belong chiefly in two clans, the granite 

 and gabbro; the first among the visible rocks is mainly intrusive, 

 the latter essentially extrusive (basalt). The diorite clan is also 

 essentially extrusive (andesite), while the visible alkaline rocks 

 (including the syenite and monzonite clans) have a volume less 

 than one per cent of that of the subalkaline ones. These facts 

 are considered to -be of fundamental importance. After a brief 

 discussion showing that qualitatively all the important clans are 

 found in the different grand divisions of geologic time, attention 

 is called to the persistence of the gabbro type, a prominent fact. 

 Then follows a classification of intrusive bodies: first those pro- 

 duced by simple injection, such as laccoliths, and then those 

 formed by replacement, like batholiths, followed by a chapter on 

 extrusive masses, one type of which, it is suggested, may be the 

 exposed portions of batholiths. 



Part two of the book outlines a general theory for igneous 

 rocks, beginning with a discussion of the composition of the 

 earth in which an upper outer granitic shell resting on a lower 

 basaltic one is assumed. Then follow chapters sketching the 

 processes of abyssal injection of the lower basalt into the gi*an- 

 itic shell. The method of intrusion by magmatic stoping is 

 fully treated, which process involves the assimilation of the 

 engulfed material and leads to the belief of the secondary origin 

 of much rock-magma. The theoretical side of magmatic assimi- 



