No. 411.] REVIEWS OF RECENT LITERATURE. 239 
measures the dark components of the rock mass. In the norite 
F= 19.78, vig, FeO = 7.38 + MnO —.36 + MgO —8.15, and the 
remainder of CaO left after subtracting 4.73 CaO (the amount 
necessary to combine with the 4.73% of Al,O, in group C) from 
8.65 CaO, the amount shown in the analysis. The relation of the 
alkalies to one another is indicated by the letter 7, which is given a 
value corresponding to the proportion the NaO bears in the analysis 
to the total alkalies calculated to the unit ro. In the above analysis 
the Na,O is to K,O as 4.23 is to 1.39, or as 7.5 is to 2.5. 7 thus 
is 7.5. The formula of the rock is 
S 2s BO. 5O, A -—ts2, Cup F — 19.78, n= 
In the plotting the absolute values of 4, C, and ¥ are not used, 
but instead their proportions are calculated to a total of 20 units, 
and these ratios are made use of. The values 5.62, 4.74, and 19.78 
are as 4: 3: 13 in the scale of 20, and the simplified formula is 
559-5 @4 Ca fis, 27-5 This formula not only expresses the approximate 
chemical composition of the rock for which it is calculated, but it 
expresses also roughly the proportions of alkaline feldspars, lime 
feldspars, and dark components present in it, and from the formula 
may be calculated the analysis. The ratios a: c: fare represented 
in a triangular projection by a dot, the position of which discloses at 
a glance the chemical character of the rock it represents. „Rocks 
of similar composition are represented by groups of dots in certain 
portions of the triangle, and these groups are observed to fall natu- 
rally into subgroups. The discussion of these features is reserved by 
the author until after he has plotted the effusive rocks. The present 
paper deals exclusively with rocks possessing the granitic texture. Of 
these the author has investigated over 200. He has recalculated the 
proportions of each of the analyses and has plotted them in a series 
of projections. A final projection contains all the types and thus 
serves as a summary of the work. Among the rock analyses studied, 
40 are of granites, 36 of syenites, 37 of diorites, 28 of eleolite-sye- 
nite, 27 of gabbros, 23 of essexites and theralites, 4 of iolites and 
other rare basic rocks, and 11 of peridotites. 
Moses and Parsons, Elements of Mineralogy, Crystallography, 
and Blowpipe Analysis, etc. — The new edition of Moses and 
Parsons’s Elements of Mineralogy covers concisely the greater part 
of the field of mineralogy. As its title indicates, it not only treats 
Moses, A. J., and Parsons, C. L. Elements of Mineralogy, So 
and Blowpipe Analysis, from a practical standpoint, including a description 
