166 Bevietvs — Professor H. A. Miers' Mineralogy. 



and form of crystals; it does not pretend to be exhaustive, and 

 the mathematical relations, though clearly and briefly set forth, ar& 

 not brought into prominence, nor are any detailed examples given in 

 the methods of calculating crystals. About half (38 pages) of this 

 chapter is occupied by a description of the different crystal-systems ; 

 22 of the 32 classes are described, all those, that is to say, which are- 

 unquestionably represented among minerals. A complete list is 

 given in an appendix at the end of Part I. The names employed in 

 Dana's textbook for the crystal-classes (e.g., calcite class, cuprite 

 class, etc.) have been wisely adopted in place of the unnecessarily 

 long and confusing names (different in every author) which one 

 finds elsewhere. 



In the appendix on the crystal-classes, names of the latter type 

 are employed, and like other authors, the present one has not 

 refrained from inventing new terms to denote the different types of 

 symmetry, some of which (e.g., alternating, equatorial, central) seem 

 desirable innovations. This lack of uniformity in nomenclature i& 

 doubtless unavoidable in a science which has not been standing still, 

 but it is none the less much to be deprecated. In this connection 

 we may remark that, according to the preface, Dana's mineral names 

 have been adopted ; in the text, however, are to be found fluor, 

 pyrites, blende, anatase, copper-glance, mispickel and other names- 

 not used by Dana. 



In the portion on geometrical crystallography there are short, but 

 useful, chapters on vicinal faces and light figures, and on etched 

 figures, the relation of which to the symmetry of the crystal i& 

 specially pointed out. In the appendix above mentioned the 

 symmetry of the 32 classes is indicated by diagrams giving the 

 general forms of etched figures. A brief and clear account of space- 

 lattices is given in an appendix dealing with theories of crystal- 

 structure. 



The optical properties of crystals are treated in almost as much 

 detail as the geometrical relations, and should be of value to the 

 student. As remarked in the preface, however, the introduction of 

 both Fresnel's ellipsoid and the indicatrix may be at first somewhat 

 confusing. Of the remaining chapters in Part I, that dealing with 

 the relations between the properties of minerals may be specially 

 mentioned ; the remarks on solid solutions, for example, are such as- 

 are to be found in no other general textbook of mineralogy. 



In Part II, devoted to descriptive mineralogy, no attempt has been 

 made to give a complete list of all the perfectly or imperfectly 

 known mineral species. The author's aim has been rather to 

 give a readable and detailed description of certain minerals selected 

 as types, and to compare other less important species with these 

 types. Kare minerals are sometimes mentioned with the object of 

 elucidating the inter-relations of groups, but no doubtful minerals 

 receive mention. At the head of the description of each type-species- 

 is printed in smaller type an enumeration of the principal characters 

 of the species, an arrangement useful for purposes of reference. In 

 place of the usual list of localities is given a description of the mode 



