LITERARY NOTICES. 



133 



inorganic and those of organic nature are 

 divided into a descriptive and a philosophi- 

 cal group. In writing the six succeeding 

 essays it was the author's design to bring 

 together in a concise form the facts and the 

 reasonings from which are deduced what he 

 regards as the principia of geogeny, geog- 

 nosy, and mineralogy. The chemistry of 

 the atmosphere, and the relations of the 

 earth's aerial envelope both to outer space 

 and to the gases condensed, and the waters 

 precipitated on the surface of the globe, are 

 set forth in the third and fourth essays, as 

 a preliminary to the study of rock-masses. 

 In the next three essays the genesis and 

 the geognostic relations of the various crys- 

 talline rocks are considered ; and finally the 

 decay of these, which has determined their 

 present surface-outlines, and has given rise 

 to the materials of the uncrystalline sedi- 

 mentary strata. In the fifth essay, Pro- 

 fessor Hunt attempts to show the defects of 

 the several other proposed explanations of 

 the origin of the crystalline rocks, and sets 

 forth his crenitic hypothesis, according to 

 which they have been derived for the most 

 part indirectly and by aqueous solution 

 from a single primary plutonic mass. These 

 and other related points are more fully dis- 

 cussed in the sixth essay. 



A system of classification for the min- 

 eral species composing the earth's crust, 

 which should consider their physical char- 

 acters in connection with their chemical 

 composition, and the mode of formation of 

 mineral species, has seemed to the author 

 for many years to be a desideratum. What 

 he believes to be a natural classification of 

 the native silicates is included in this vol- 

 ume, and is followed by an outline of the 

 system as applied to all other native min- 

 erals. Regarding the silicates as a natural 

 order, Professor Hunt divides them into 

 three sub-orders: those without alumina, 

 which he calls prolosUicales ; those with alu- 

 mina and containing combined protoxides, 

 protopcrsilicates ; and those with alumina, 

 but no protoxides, persilicates. These sub- 

 orders are divided each into five tribes, ac- 

 cording to distinctions of structure, hard- 

 ness, and density. Each tribe is made up 

 directly of species. The silicates are in- 

 cluded in the same class with the oxidates, 

 titanates, niobates, tantalates, tungstates, 



molybdates, chromates, vanadates, antimo- 

 nates, arsenates, phosphates, nitrates, sul- 

 phates, borates, carbonates, and oxalates. 

 This class is numbered II ; Class I com- 

 prises the metallates ; Class III, the haloid- 

 ates ; and Class IV, . the pyricaustates, or 

 combustible species. The author has in 

 preparation a treatise on mineralogy which 

 will be a complete presentation of this 

 system. 



The next essay deals with the geologi- 

 cal history of pre-Cambrian rocks, both in 

 North America and in Europe, and is mainly 

 a condensation from the account given in 

 the author's volume on " Azoic Rocks." In- 

 timately connected with this subject is the 

 history of serpentines, which is sketched in 

 the following essay. The various opinions 

 as to the geognostical relations of serpen- 

 tines which have been held by different 

 writers are shown, and the author's reasons 

 for maintaining their aqueous origin are 

 given. In the concluding essay, the ques- 

 tion of the Taconic rocks is discussed at 

 some length. The eleven essays which are 

 collected in this volume are papers which 

 have been presented to American and Brit- 

 ish learned societies, and have been pub- 

 lished in their transactions and in scientific 

 journals. Changes have been made occa- 

 sionally in revision, but all additions of im- 

 portance are inclosed in brackets. 



Annual Report of the Chief Signal-Offi- 

 cer of the Army for the Year 1885. 

 Washington : Government Printing-Of- 

 fice. Two vols. Pp. 609, 440. 



The course of instruction pursued at 

 Fort Meyer has been enlarged and other- 

 wise improved, and now provides for theo- 

 retical and practical instruction in the du- 

 ties required of the Signal Corps in time of 

 war. Lectures by professors of meteorol- 

 ogy have been provided for ; and a course 

 of instruction in military surveying, field- 

 sketching, and topographical drawing has 

 been added. A text-book of meteorology 

 has been prepared by Professor William 

 Ferrcll, and forms the second part of the 

 present report. Professor Cleveland Abbe 

 has in preparation a treatise on the theory 

 of instruments used in meteorology. Trans- 

 lations of papers on temperatures and 

 storms by Ragone and Wild are appended ; 

 and translations have been made of impor- 



