REVIEWS ^5 



reference to Schone's work. The treatment of rock texture contains a com- 

 mendable criticism of the idea of " order of crystallisation," which has per- 

 meated petrographic work for so long ; it cannot be too strongly emphasised 

 that, owing to the fact that minerals in rocks consolidate through temperature 

 ranges, and that the order in which they appear, in solid form, depends on the 

 physico-chemical conditions prevailing, there can be no such thing as a 

 " normal order." In this chapter, however, the discussion of crystallites is 

 misleading, since it is based on Vogelsang's classification, which is now gener- 

 ally regarded as defective, while the statement on page 352 that in graphic 

 granite, quartz and felspar are present in eutectic proportions likewise requires 

 correction, as it has been shown that this structure cannot be a eutectic. 

 While the chapters on analysis contain no description of the chemical methods, 

 a large mass of somewhat heterogeneous information is included. The 

 discussion of equilibrium diagrams and mineral systems is too brief to be of 

 much utility, while the reference to the necessity for the determination of 

 titanium dioxide (p. 380) is rather belated, as this oxide has been generally 

 determined in rock analyses for the past decade. 



While the author in places has perhaps gone beyond the limits of his title, 

 the book can unhesitatingly be recommended as a mine of information on 

 the subject, the lucid treatment and clear discussions greatly enhancing its 

 value from the point of view of the student. In future editions the rather 

 large number of misprints might be corrected, the most notable being the 

 omission of a line on p. 484, while some of the mathematical symbols, notably 

 the signs for square root on p. 473 and 492, are by no means clear. A. S. 



Catalogue of the Fossil Bryozoa (Polyzoa). The Cretaceous Bryozoa 

 (Polyzoa). Volume III : The Cribrimorphs. Part I : By W. D. 

 Lang, Sc.D., F.G.S. [Pp. 269 + ex, with 8 plates and 115 text- 

 figures.] (London : British Museum Natural History, 192 1. Price 

 £1 los.) 



It is difficult, within the limits of a short review, to do justice either in apprais- 

 ing or criticising a detailed work of this nature. The second of these can be 

 done quite briefly, for it mainly concerns matters of preference. We think 

 it is rather a pity that the term Bryozoa is used instead of the more familiar 

 Polyzoa. While it is not fair to imply that recent forms are not considered 

 in this work, yet at the same time we cannot help feeling that, in the literature 

 of the Polyzoa in general, and perhaps here also, too sharp a separation is 

 kept between living and fossil forms. 



|fe The book is divided into two portions : I. Introductory, and II. Systematic. 

 The second part is a very careful list of the large collection of Cretaceous 

 Cribrimorphs in the possession of the British Museum. Of each species the 

 author gives a full synonymy, the diagnostic characters, a description, the 

 distribution, a list of the individual specimens in the collection, and frequently 

 also critical remarks. Useful keys to the sub-families, genera, and species 

 are provided. These, with the full index and splendid drawings of Miss G. M. 

 Woodward, add much to the value of the work. This portion of the volume 

 has evidently involved a great deal of labour. As this is the first work that 

 deals with the Cretaceous Cribrimorphs as a whole, it is sure to be in great 

 demand by all students, and can well serve as a model for workers in allied 

 fields of study. 



The introductory part of the book is also valuable, and should be read by 

 anyone engaged in the difficult task of a detailed systematic study of any 

 group of animals. It may be that experts on these matters will difEer from 

 the author in regard to some of his interpretations or of his application of 

 certain theoretical principals to particular cases. This much, however, is 

 certain : the author has done his utmost to set forth the ideas that have 

 governed his treatment of the subject, and has succeeded in doing so clearly 



