Reviews — G. P. Iddings — Problem of Volcanism. 333 



for the origin of the great oceans, for he thinks that they overlie 

 relatively large and dense planetismals, which have been welded with 

 the substance of the growing earth. These dense accretions he 

 recognizes not only through the sagging of the earth's surface above 

 them, and the influence they exert upon the plumb-line, but also 

 more directly through the products of their volcanoes. He maintains 

 that there are two great provinces of igneous rocks, the Oceanic and 

 the Continental respectively. What may be termed the average 

 igneous rock of the former has a density of about 3*00, and of the 

 latter 2*85. The Atlantic and Pacific hordes of various authors he 

 dismisses as "highly artificial misnomers". 



A difficulty which must occur to anyone in considering the 

 application of Iddings' hypothesis, even in America, is the continental 

 distribution of the Columbia River Basalts. This point is dealt with 

 in advance as an example of the danger of loose petrographical 

 nomenclature. Iddings takes two analyses, representative of large 

 masses in the so-called basalt series, and recognizes in both a decidedlv 

 andesitic flavour. The treatment of the matter is too condensed to be 

 satisfactory, and one wonders why the predominantly basic magmas 

 (according to general belief) of Iceland and the Hebrides, of the 

 Deccan, and of the Zambezi region, to take well-known examples, are 

 not referred to. The Zambezi lavas are of great geological antiquity, 

 and once we step back to consider such ancient products another lion 

 is met with on the path. How is it that Scotland in Old Red Sand- 

 stone times furnished a typical continental suite of igneous rocks, 

 and in New Red Sandstone times an equally typical oceanic suite ? 

 One might be tempted to argue that in this case an ocean basin had 

 not been permanent, were it not that the lavas of New Red Sandstone 

 age were erupted on a desert and many of their cracks and vesicles 

 contemporaneously choked with millet-seed sand. 



As might be expected from the foregoing, Iddings does not follow 

 Daly in his speculations. For Iddings, the igneous rocks of a district 

 afford a sample of the deeply buried foundation stones. During its 

 upward progress the magma is frequently separated into more or less 

 dissimilar fractions by differentiation, but is practically never polluted 

 by assimilation. 



In a short review it is impossible to follow our author further. 

 A reader who enjoys a plunge into a sea of doubt is recommended to 

 dip into the pages of this book. He is sure to be stimulated for 

 a time, but, if in stature like the present writer, he will find it 

 wearisome before long to be so continually beyond his depth. 



One last point may be noticed. In the construction of a book of 

 comprehensive aim it goes without saying that all available sources 

 of information have not been consulted. Still, it is surprising to find 

 that Heim's later writings have made so little impression that 

 a ' double fold ' is reproduced from the Ifechanismus to illustrate 

 Alpine structure. 



E. B. Bailey. 



