REVIEWS 493 



the work of E. S. Fedorov which have not yet found their way into easily 



accessible literature. 



In the same way the protractor advised embodies the principles of those of 

 Hutchinson, Fedorov, and Penfield, and although rather clumsy and com- 

 plicated, serves the purpose of several ordinary auxiliaries. However, habit 

 is too strong for us to expect any but youthful enthusiasts to adopt its use. 



The principles of stereographic and gnomonic projections (including the 

 very important Angle-point or Winkelpunkt) are set forth briefly, and a 

 rather arbitrarily chosen set of problems and examples appended. The 

 relation between indices and reticular densities referred to as Mallard's 

 Theorem just borders on crystal structure. Once again the advantages of 

 gnomonic over stereographic projections and of two (and three) circle over one 

 circle goniometry are vindicated ; two circle goniometry is solid geometry 

 compatible with solid figures and naturally adapted for projection, while the 

 gnomonic projection is superior to the stereographic for determination of indices 

 and crystal drawing. 



In computation the cotangent form of the Anharmonic Ratio, and 



particularly the Harmonic Ratio, is employed rather than the more usually 



adopted sine form and a set of tables added, like the Hutchinson slide rule, to 



tan X p 

 solve the formula = - . Its application is abundantly demonstrated, 



and an especially interesting case is the rhombohedral system. Considering 

 the nature of the book some of the smaU type print on the accuracy of graphical 

 methods might have been given greater prominence. 



The chief points of the new system turn on a preference for fundamental 

 measured angles rather than theoretical calculated values of axial ratios and 

 angles — a suggestion justly vindicated by the anorthic system. An outline 

 of standard methods for investigation and description is given which should 

 prove invaluable as a groundwork and guide to future crystallographers, and 

 though new suggestions of systematic methods take long to become universally 

 adopted, the book is based on sound practical lines. 



Edgar D. Mountain. 



Geology o! Non-metallic Mineral Deposits other than Silicates. Vol. I. 

 Principles of Salt Deposition. By Amadeus W. Gragau, S.M., S.D. 

 [Pp. xvi + 435, with 125 text figures.] (New York: The McGraw 

 Hill Book Co., Inc.) 



This book is the first volume of a treatise which is intended to deal with those 

 non-metalUc minerals usually designated as " salts," the term being used 

 in a sense sufficiently wide to include the hahdes, sulphates, nitrates, phos- 

 phates, carbonates, borates, and so forth. An attempt is made, on the 

 basis of known geological relationships combined with results of synthetic 

 work in the laboratory, to elucidate the conditions of formation of such 

 deposits. The amplification of field work by laboratory investigations during 

 the past forty years has greatly increased our knowledge of the geology of 

 such salts ; for example, the classical work of Van 't Hoff and his colleagues, 

 based on phase-rule investigation of the particular substances concerned, 

 has yielded a fund of information concerning the origin of oceanic salt deposits. 

 The volume under review is confined to an examination of the principles 

 of the deposition of these salts, especially with reference to those now forming, 

 the application of these principles to the problems presented by the older 

 deposits being deferred to a later volume. The first two chapters are of an 

 introductory nature, the first one treating, in an elementary way, the chem- 

 istry of the salts, while the second gives an account of the characteristics 

 and occurrences of the more important salts. The inclusion, in the latter, 

 of such terms as " halo-carnallite " or its synonym " carnallitite " for the 

 entectic mixture of halite and carnallite, is to be deprecated ; this entectic 



