426 Reviews — The Nomenclature of Petrology. 



type, comprising volcanic, plutonic, and hypabyssal phases, 

 obviously derived from a common magmatic basin. The intrusives 

 also give evidence of a certain amount of magmatic differentiation 

 in the form of leucocratic and melanocratic facies, with aplites and 

 pegmatites. 



The Nomenclature of Petrology. By Arthur Holmes, D.Sc, 

 A.R.C.S., F.G.S. pp. 284. London : T. Murby & Co. 1920. 

 Price 12s. 6rf. net. 

 OOME years ago the author began to compile a card-catalogue 

 ^ of petrographic terms for the use of students at the Imperial 

 College of Science ; in view of the usefulness of this catalogue and 

 in response to many suggestions he has now developed and published 

 it in a handy form. 



In the Introduction of twenty-one pages the subject of petro- 

 graphic nomenclature is discussed in general terms, and with the 

 author's remarks as to its complexity and the unnecessariness of 

 many of the names employed by various authors we are in hearty 

 agreement. Some petrologists really seem to have gone out of their 

 way to coin cumbersome and jaw-breaking names, almost impossible 

 to remember or to spell, and conveying nothing as to the actual 

 character of the rock. In view of the Committee on Petrographic 

 Nomenclature now sitting it would be unseemly to enter into a 

 general discussion of the principles to be adopted in the future, but 

 the author's temperate statement of his views may be read with 

 profit by all petrologists. 



The greater part of the book naturally consists of a glossary or 

 dictionary of petrographic terms, including structures and properties 

 as well as types, and including those referring to igneous, sedimentary, 

 and metamorphic rocks. Under each heading a brief definition is 

 given, with in many cases the name of the introducer of the word 

 and one or more references to the literature. The list appears to be 

 comprehensive and well selected ; a few more explanations might 

 well have been given of terms employed in economic geology, as by 

 miners, and in the records of bores. Thus we find that most of the 

 Scottish terms are included, while their English equivalents appear 

 to be omitted. We confess that it is very difficult to give any precise 

 definition of many of these words, owing to the vagueness of their 

 use ; they are, however, very puzzling to students and might well 

 have been included with some sort of explanation, even if only a 

 statement that they cannot be defined precisely. In this connexion 

 we are pleased to note that the author invites suggestions from 

 petrologists as to terms to be included in another edition. 



Some useful appendices are added to the text, giving glossaries of 

 the more common and important French and German petrological 

 terms, lists of Latin and Greek words and prefixes, and tables of 

 classification, the latter being largely based on the so-called degree of 

 satulration of the rock, as suggested by Shand. Although we have 



