REVIEWS 785 



have omitted the values of the bi-refringence, for although of prime importance 

 in the case of cleavage flakes bounded by parallel planes it is of little value for 

 irregular grains of which the thickness cannot be determined. The author has 

 placed in deserved prominence the determinative methods of Schroder van du Kolk 

 and Becke, and has added a list of most useful oils which can be used to ascertain 

 the mean refractive index of the minerals he mentions. It is doubtful, however, 

 whether a solution of sulphur in methylene iodide can be made to attain such 

 a high refractive index as i"83 and retain any degree of stability. The usual 

 figure is nearer 179. 



The Petrology of the Igneous Rocks. By F. H. Hatch, Ph.D. [Pp. xxiv+454.] 

 Seventh Edition. (London : G. Allen & Co., Ltd., 1914. Price ys. 6d. net.) 



The seventh edition of this useful textbook differs mainly from the older editions 

 in the presence of chapters on the Pyroclastic Rocks and the Metamorphic 

 Derivatives of the Igneous Rocks, which, although treated very briefly, are well 

 done, and in keeping with the rest of the book. The classification of Igneous 

 Rocks adopted by Hatch is, however, still shaped by the old qualitative views, in 

 spite of the recent onset of quantitative treatment. It is based mainly on silica 

 percentage, followed, at least in the case of plutonic rocks, by a subdivision into 

 alkalic, monzonitic, and calc-alkalic series. It is difficult to see why the ultrabasic 

 rocks should be excluded from this scheme (p. 160) if it is adequate to the needs 

 of students and petrographers. A rather elaborate quantitative treatment is 

 accorded to the acid plutonic rocks, but it is denied to the more basic. Whilst 

 the volcanic rocks are subdivided on the same basis as the plutonic, the hypabyssal 

 types are apparently not considered as susceptible to this treatment, and are 

 classified into five vaguely defined families. This classification is a patchwork 

 consisting of oddly contrasted compartments in which qualitative and quantitative 

 treatment is alternately adopted. While there is, no doubt, still some advantage 

 to be gained by the student in continuing with the older qualitative classification, 

 it is time the newer quantitative ideas were appearing in the textbooks. The 

 description of the rocks and the account of their distribution is in general 

 excellently done. When Scottish Carboniferous basalts are mentioned in several 

 places it is difficult to understand the repetition of the ancient error that andesites 

 occur amongst them (p. 413). The terms "texture" and "structure," which now 

 possess well-defined and different significations, are used as though they were 

 interchangeable. The book is free from typographical errors, but the word 

 "spilosite " is used where " spilite " is obviously meant (p. 29). 



Text-Book of Paleontology. Edited by Charles R. Eastman, A.M., Ph.D., 

 Prof, of Paleontology, Pittsburg. Adapted from the German of KARL A. 

 VON Zittel. Second Edition, vol. i. [Pp. xi-f 839, illustrated.] (London 

 Macmillan & Co., Ltd., 1913. Price 25s. net.) 



Almost the only fault we have to find with this admirable volume is the spelling 

 of the title, an atrocious Americanism, which, together with "Paleozoic" in the 

 text, is enough to make a classically educated Englishman lose his temper. It is, 

 moreover, an insult to the memory of the great German palaeontologist upon whose 

 work the present and previous editions are based. 



The present volume, which deals solely with the invertebrates, is considerably 

 larger that its predecessor in the first edition (1899), containing 839, against 706, 



