Reviews — A Neio Rock-Classification. 173 



and Professor Martin for examining the shells ; and to Dr. Schroeder 

 van der Kolk for assisting in the microscopic study of the rocks. 



In the preface to the English edition Dr. Molengraafif specially 

 thanks Dr. G. J. Hinde for reading the proofs and revises, and to 

 this supervision may perhaps be attributed the general ateence of 

 errors in the text, which are usually too prominent in translations 

 printed abroad. A separate vocabulary of Dyak names of places 

 and things (most of which are given in notes or in the text and index, 

 but not collectively) would have proved of service to English readers. 



We commend the work to all who are interested in the geology 

 of the East Indies, and hope it will find a place in all the public 

 reference libraries in Britain and America and the Colonies. 



IV. — A New Eock-Classification. 



Quantitative Classification of Igneous Eocks, based on 

 Chemical and Mineralogical Chakacters, with a Systematic 

 Nomenclature. By AVhitman Cross, Joseph P. Iddings, 

 Louis V. Pirsson, Henry S. Washington. 8vo ; pp. 286. 

 (Chicago, 1903.) 



THE classification of the igneous rocks is a question which has 

 engaged the attention of many petrologists ; and, as a wide 

 divergence of opinion sufficiently attests, it involves problems of 

 much difficulty. The memoir before us is the joint production 

 of four well-known American authorities, and represents, we are 

 told, an exhaustive discussion of the subject extending over many 

 years. Moreover, it is not merely a contribution to a vexed question, 

 but aims at affecting a final settlement of it. For these reasons the 

 scheme put forward, and the arguments upon which it is based, 

 demand a frank and careful consideration. 



Our authors start from the proposition, which will scarcely be 

 disputed, that existing methods of classification are illogical and 

 in many respects unsatisfactory. But we are by no means convinced 

 that they have correctly diagnosed the imperfections of the schemes 

 in present use ; and on such diagnosis the success of any proposed 

 remedy must necessarily depend. The confusion which prevails in 

 the classification of igneous rocks is in some measure due to causes 

 inherent in the nature of the subject-matter, and especially to the 

 absence of any well-defined ' species,' such as constitute the units of 

 classification in the sister sciences. But the present difficulty is, as 

 it appears to us, attributable in a much greater degree to the rapid 

 and unequal growth of the science of petrology. Fifty years ago 

 the classification of igneous rocks was of the crudest kind, but it 

 seems to have been quite adequate to the state of knowledge at that 

 time. The great revival of petrographical research which followed 

 the introduction of microscopical methods has instigated a large 

 body of workers, and the annual output, especially from the German 

 laboratories, has attained a very considerable volume. The great 

 bulk of this work is of a purely descriptive kind — petrography in 



