Geology and Mineralogy. 89 



that anorthite is to be regarded, not as an orthosilicate, but as a 

 metasilicate. Later papers on the same general subject (Sitz- 

 ungsberichte Akad. Wien cxiv(i), 455, 1905, cxv(i) 'Feb., 1906), 

 discuss the matter in more detail. The conclusion is reached 

 that while willemite and monticellite are to be regarded as ortho- 

 silicates, olivine is a metasilicate, and the acid present in garnet, 

 epidote, zoisite and prehnite is H 4 Si 3 8 ; the formula of olivine 

 would be written (MgOMg)Si0 3 . 



9. An Introduction to Chemical Crystallography ; by P. 

 Geoth, Authorized Translation bv Hugh Marshall. Pp. vii, 

 123. Xew York, 1906 (John Wiley & Sons).— The Chemical 

 Crystallography of Professor Groth was noticed about a year 

 since when the German edition was issued (see vol. xix, p. 467). 

 We have now an authorized English translation made by Dr. 

 Hugh Marshall of the University of Edinburgh. This will be 

 found very useful by the English-speaking public and will extend 

 the sphere of usefulness of this valuable work. The translation 

 has been prepared in cooperation with the author, who has super- 

 vised the proof-sheets. It follows the original closely and adds 

 occasional references to original papers or abstracts which have 

 appeared in the Journal of the Chemical Society. 



10. Geometrische Kristallographie • by Ernst Sommerfeldt. 

 Pp. 139, with 31 Tafeln and 69 text-figures. Leipzig, 1906 

 (Wilhelm Engelmann). — Those interested in the problems of 

 modern crystallography, handled particularly from the theoreti- 

 cal side, will find much of value in the present work. A series 

 of thirty-one ingeniously constructed plates at the close of the 

 volume present, in a novel way, the symmetry conditions and the 

 relations of the existing forms to each other. 



11. JEtude sur VJLttat actuel des 3fi?ies du Transvaal : Les 

 Gites — Leur Valeur, &nde inditstrielle et financihre ; by George 

 Moreau. Pp. 218, with 48 figures. Paris, 1906 (Librairie 

 Polytechnique, Ch. Beranger, Editeur).— This is a useful work to 

 those interested in the mines of South Africa, giving a descrip- 

 tion of the country and its geology with particular reference to 

 the Witwatersrand; a lull discussion of methods of exploitation 

 adopted is added. The author speaks enthusiastically of the min- 

 eral resources of the Transvaal and its possibilities, although he 

 recognizes some of the limitations to its development which 

 unavoidably exist. 



12. Anleitung zum Gebrauch des Polarisationsmikro shops ; 

 von Dr. Erxst Weinschenk. Pp. vi, 147, with 135 figures. 

 Zweite, umgearbeitite und vermehrte Auflage. Freiburg im 

 Breisgau, 1906. (Herdersche Verlagshandlung. Zweignieder- 

 lassungen in Wien, Strassburg, Miinchen, und St. Louis, Mo.) — 

 An excellent presentation of the polarization microscope in its 

 different parts, with the various methods of investigation applica- 

 ble to it and the principles involved in their use. It is well 

 illustrated and gives, in small compass, just the information 

 needed by students of the subject. It should be in the hands of 

 every one concerned with this field of investigation. 



