158 SCIENCE PROGRESS 



other principles. At the present time most new rock species are named 

 after the locahty in which the rock is first discovered, a method which has 

 obvious disadvantages. Such terms as garewdite, fasibitikite, and onkilonite 

 are merely a tax on the memory and fail to give any suggestion of their con- 

 notation. Numerous attempts to systematise the nomenclature have been 

 made, but all may be said to have failed. The announcement of Dr. Holmes's 

 book raised hopes that a more successful effort was about to appear, but such 

 hopes have not been realised. The title of the book is a misnomer, as practi- 

 cally no attempt at clearing up the question is made. A more appropriate 

 title would have been a " Glossary of Petrological Terms," for the book is 

 little more. 



The appearance of such a glossary, however, is welcome, as most of the 

 existing ones are somewhat out of date, and many new names have been 

 introduced in the past few years. The definitions, so far as can be judged, 

 are accurate and include not only rock-names but practically all the petro- 

 graphic terms referring to structure, texture, mode of origin, and so forth. 

 While no omissions of importance have been noted, future editions might 

 include such terms as "clunch," "crowstone," "bullion," "fhnt-clay," and 

 " gaize," which, though perhaps local in their application, are yet freely used 

 in memoirs and papers. 



While the reader is referred to Loewinson-Lessing's Lexique petvogyaphique 

 for the original papers in which many of the terms are defined, a series of 

 recent references is appended to the definition of each term. Although in 

 general the references are well chosen, the selection in a few instances is 

 difficult to understand, important papers being omitted where others of less 

 importance are inserted. For example, under " Fireclay," no mention is 

 made of Mellor's work on the constitution of that rock, while Bowen's work 

 does not appear under " Petrogenesis." 



To those geologists who are not specialists in petrography, and to students 

 the book should prove of great value, as much of the information could only 

 be obtained by a diligent search through the literature. The author is to be 

 commended, both for the accuracy and the completeness with which he has 

 carried out his work. A very useful appendix of French and German terms, 

 with their English equivalents, appears at the end of the book. Misprints 

 are few and unimportant, the most noticeable occurring on pages 62, 76, 147, 

 and 201. 



A. S. 



Notes on Geological Map-reading. By Alfred Harker. [Pp. 64, with 40 

 text-figures.] (Cambridge : W. Heffer & Sons. Price 35. 6d. net.) 



To the student of geology the subject of map-reading is of such importance 

 that it is impossible for much progress to be made without a clear understand- 

 ing of geological maps and their interpretation. Mr. Marker's book is written 

 from the point of view that all the information contained in a geological map 

 is to be read off directly, the drawing of sections being merely for the 

 purpose of illustration. Despite the fact that an elementary knowledge of 

 geometry is all that is required for the interpretation of such maps, students 

 often find themselves in difficulties. This book should go far to dispel these 

 difficulties, as the methods described are such as to eliminate the necessity for 

 using trigonometrical formulae, or even a protractor. After a preliminary 

 discussion of typographical maps, the author deals with geological ones, in 

 stages of increasing complexity, so that finally the reader should be capable of 

 interpreting any published map. The descriptions are exceedingly lucid, and 

 the diagrams which illustrate the methods very clear. 



A. S. 



