Reviews — Dr. M. E. Wadsirorth — Lithological Studies. 269 



or without nickel. As we recede from the centre, pyrrhotite is 

 united with these ; then olivine, enstatite, and sometimes diallage, 

 in varying proportions, are the chief constituents. From this zone 

 we pass into the basaltic rocks, then into the andesites, lastly into 

 the various representatives of the most acid rocks. But, owing to 

 various causes, these original zones have been much disturbed and 

 mingled, so that at the present time a definite and regular sequence 

 of igneous rocks is hardly to be expected. The author passes on to 

 consider the question of whether the so-called igneous rocks are 

 portions of the original magma of the earth or of sedimentary 

 deposits in a condition of aqueo-igneous fusion. Dealing with this 

 question after a strictly logical method, he shows that the latter view 

 rests rather on hypothesis than on fact : to it " the field evidence, as 

 well as the microscopic, is opposed in toto." Dr. Wadsworth also 

 repudiates the attempt to classify igneous rocks by their geological 

 age, while he admits, of course, that lapse of time has in many cases 

 produced subsequent modifications, and there is a possibility that 

 some peculiar conditions prevailing at the time of consolidation may 

 have had an influence. Some valuable remarks are then made upon 

 certain of the more important rock-structures, as joints, cleavage and 

 foliation, and on misconceptions which have arisen concerning them. 

 The author then passes on to consider the chemical analysis of rocks, 

 prior to which he points out the frequent misuse of this mode of 

 investigation, due to neglect of the past history of the rock and of pro- 

 per precautions in selecting specimens for analysis. An interesting 

 critical sketch is given of the history of opinion in regard to the 

 species of the felspar group of minerals, the author coming to the con- 

 clusion that " a systematic classification cannot properly be based 

 on any such variable, indeterminate materials." In his opinion a 

 similar relation and a like variability seems to exist in the enstatite- 

 hypersthene-pyroxene-amphibole group of minerals. The author 

 then states his views as to the principles upon which a rock 

 classification should be founded. These are too lengthy for quotation 

 in the space of a brief notice, but the following extract may be given 

 as indicating the dominant principle : " All the petrological, litho- 

 logical, and chemical characters should be used in determining rock 

 species ; that is, the rock as a whole and in all its relations should 

 be considered. The classification should be a natural one, and 

 therefore empirical, embodying all known characters of the rocks." 



The second chapter in the volume deals with the Siderolites and 

 Pallasites. The former name is applied by the author to rocks 

 composed chiefly of iron — either native or in its secondary states, 

 as magnetite, hematite, menaccanite, etc., with or without nickel, 

 graphite, etc. It includes masses of iron and iron-ore that have 

 fallen as meteorites, with some of eruptive origin, but excludes veins 

 or chemical deposits of iron-ore. The name Pallasite is given to 

 masses of iron (perhaps oxidized) containing olivine and occasionally 

 felspar, enstatite, diallage, etc. Those at present recognized apj^ear 

 to be of meteoric origin, but Dr. Wadsworth regards a variety, to 

 which he gives the name Cumberlandite, as eruptive. 



