230 



KNOWLEDGE. 



June, 1913. 



Economic Woods of the United States. — By Samuel J. 

 Record, M. A., M.F. 117 pages. 6 plates. 9^-in. X6-in. 



(Chapman & Hall. Price 5/6 net.) 



This book is most complete for a somewhat condensed work 

 on the subject, and is offered at a very reasonable price. It 

 refers to U.S.A. timber trees onlv, but a large number of these 

 are important to us owing to their commercial uses and also 

 in several cases to their value for planting in this country. 

 The book is well arranged; each point is dealt with in a 

 businesslike and concise manner, and with as little repetition 

 as possible. The language is clear, and it is refreshing to 

 find no peculiar American phraseology or spelling. 



Part I deals with the structural and physical properties of 

 wood, and contains much of interest to the student in technology, 

 the forester and the commercial user of timber. Although 

 many of the points arc of necessity dealt with in a somewhat 

 condensed form the ground is well covered, and after each 

 heading is given a list of textbooks referred to and from 

 which more detailed information can be procured where 

 desired. A complete list of references, including the standard 

 books of each branch, is published at the end. 



Part II is a key with photomicrographs of some of the 

 American timbers, and is useful for showing the main character- 

 istics in structure ; but it is somewhat limited in its application. 



The work, although not intended to be original, brings 

 together a mass of useful information, and, taken altogether, 

 is a welcome and valuable addition to the literature on the 

 subject. It should appeal to those who require a general 

 grasp and have neither the time nor the means to go deeply 



into every point. 



M. C. D. 



GEOLOGY. 



The Petrology <>f tlic Sedimentary Rocks. — By F. H. 



Hatch and K. H. Rastai.i . 425 pages. 60 figures. 



7i-in.X 5-in. 



(G. Allen & Co. Price 7/6 net.) 



The petrology of the sedimentary rocks has been much 

 cultivated lately, and although it was neglected in the early 

 days of the science compared with the igneous and meta- 

 morphic branches, it is now coming into its own. This book 

 represents a culmination of interest in which sedimentary 

 petrology threatens to rival the other branches in its 

 attraction for workers. The literature of the subject is large 

 and scattered, and the authors are to be congratulated on 

 their successful attempt at its collation in the book under 

 review, which is the first of its kind. The title scarcely 

 records the scope of the work, since the majority of rocks 

 usually treated as metamorphic are also described. The term 

 '" iiietamorphisin " is used in its widest sense to indicate all sorts 

 of change in rocks, cementation, metasomatism, and 

 weathering, as well as the severer forms due to great heat and 

 pressure which result in the production of rocks included as 

 metamorphic in the narrower sense. There are certainly no 

 sharp boundaries between the various types of change, and 

 logically, therefore, the plan of the book is unassailable. We 

 think, however, that the inclusion of the metamorphic rocks 

 might have been more prominently indicated in the title; or 

 alternatively they might have been relegated to another 

 volume. i he use of the term " metamorphic " in such a wide 

 sense involves the incongruity that our typical sedimentary 

 rocks, such as sandstone, shale, and limestone, are treated in 

 the second part of the book under the heading " Metamorphic 

 Derivatives of the Sediments," and the cursory student may 

 be somewhat at a loss on finding their descriptions in this 

 place. It is to be admitted, however, that, given the definition 

 of inetainorphism here adopted, the arrangement of the book 

 is perfectly logical. 



In the first part of the book the modern sediments are 

 dealt with under the headings of " Deposition in General," 

 " Fragments! Deposits," "Chemical Deposits," and "Organic 

 Deposits." In Part II the older sediments which have under- 

 gone various types of change are described under the headings 

 " Metamorphism in General," " Cementation and Metasoma- 



tism," '* Contact Metamorphism," " Regional Metamorphism," 

 and " Weathering." In these chapters very lucid accounts of 

 the methods of deposition and the modes of change in the 

 sediments are given. In fact the book is really a well-knit 

 and concise account of the pedogenesis of the sedimentary 

 rocks. Because of this fact, and perhaps also because of its 

 limited size, the book is a liltlc disappointing on the 

 petrographical or descriptive side. Its plan also involves 

 some discontinuity of treatment for sediments which are 

 related in various ways. The calcareous rocks, for instance, 

 excluding the metamorphic types, are to be found under three 

 headings. The ordinary sedimentary limestones in general 

 appear to be inadequately described as compared with the 

 sandstones and shales. Referring to the index we find five 

 entries under " limestone," but four of these refer to 

 metamorphic types and the other to cave-limestone. In other 

 parts of the index we find additional references to crinoidal 

 limestone, dune-limestone, and dolomite, but none to oolitic 

 limestone. Then no description of the ways in which the 

 various organisms which build limestones may be recognised 

 is given. 



These, however, are but small spots on the sun of the 

 general excellence of the book, and inasmuch as the authors 

 have in our opinion accomplished what they set out to do, and 

 have produced a most interesting and important work, they 

 are entitled to all praise. They have been fortunate enough 

 to secure a most useful appendix, by Mr. T. Crook, on "The 

 Systematic Examination of Loose Detrital Sediments," in 

 which are described the methods of separating and identifying 

 minerals in small fragments. „ ... ~ 



Li. W. 1 . 



.-1 Manual of Petrology. — By F. P. Mennell. 256 pages. 

 124 figures. 9-in.X5J-in. 



(Chapman & Hall. Price 7/6 net) 



This book is based on the author's " Introduction to 

 Petrology," the second edition of which was reviewed in 

 " Knowledge " of August, 1910. It differs from the earlier 

 book in several particulars. The chapters on the origin of 

 igneous rocks and on metamorphism have been re- 

 modelled, and the position of some chapters has been 

 altered. Many of the illustrations are new, and, as a 

 whole, are decidedly better than in the former work. 

 We wish we could say the same of the classification of 

 igneous rocks adopted. Mr. Mennell "simplifies" peno- 

 logical nomenclature by classifying igneous rocks into five 

 groups according to silica percentage, and each of the latter 

 into three divisions of plutonic, intrusive, and effusive types 

 respectively. By this method he gets fifteen classes, for 

 which fourteen names are supplied, the ultrabasic plutonic 

 rocks {i.e., those with less than forty-five per cent, of silica) 

 not being provided with a name. Varieties are indicated by 

 mineralogical prefixes. It is a delusive simplification, however, 

 which reduces the nomenclature of a science, for progress or 

 increasing complexity demands an increasing nomenclature. 

 In particular the silica percentage is an extremely artificial 

 attribute on which to base a classification Thus, for example, 

 to call all plutonic rocks with a silica percentage between fifty- 

 five and sixty " diorites," and thus to include the majority of 

 nepheline-syenites, is merely to introduce confusion, just as it 

 would introduce confusion to call all marine animals " whales," 

 or all land animals " elephants," on the strength of a community 

 of habitat. 



The classification by silica percentage ignores the fact that 

 rocks are composed not of silica percentages, or of per- 

 centages of various oxides, but of minerals. Hence the 

 mineralogical variations in rocks are the most significant 

 variations, and should be those expressed in the major 

 divisions of the classification. Not less, but more, nomen- 

 clature is needed for the philosophical discussion of petrological 

 principles. What is needed is not a reckless aggregation of, 

 for example, such unlike units as nepheline-syenite and diorite 

 into one group, but a more subtle and closer characterisation 

 of igneous types leading to a more detailed classification. 



In this book the classification by silica percentage leads to 



