Leiimison-Lcssing s Classification of Rocks. 355 
usually in the same direction, but sometimes (in the basic 
rocks) they are in opposite direction — then the subdivision 
could be characterized by the use of the relation CaO:MgO. 
Curves v, Table III. These are constructed by taking as in- 
dependent variable the coefficient a and placing upon the 
axis of the y's the corresponding molecular proportions of the 
different groups of oxides. With two exceptions, ^-z-^ and i-l, 
the preceding statements are again found applicable: — the (R:;C) 
4-RO) and KO are depressed andthose of R^O and R2O3 rise. 
(In fact between the abscissas / and v the lines R2O and R^O^ 
are parallel to the axis of the x's). Antagonism appears be- 
tween R-() and RO, etc. Here may also be noted, on the dia- 
gram xvii, table II, the parallelism of the variations of R:;0 and 
Ri^Os; the antagonism of R^O and RO and the independence of 
the line of SiO:; with respect to all the other oxides. 
{Roiiark. M. Lewinson-Lessing does not say in the tex^ 
how he constructed the curves xvii, that is to say, what he took 
for independent variable; however it is apparent that he took 
RO ; but, owing to the carelessness and especially the disorder 
of the editing, and of the references, and the general presenta- 
tion of ideas, his book is very tiresome to read.) 
From p. 60 to p. 104 of the text is Lewinson-Lessing's 
characterization of eruptive rocks according to the various dia- 
grams, in the following order: Trachytes (diagrams vi and vii): 
Andesytes (diag. viii): Syenites (diagram ix); Dacytes (dia- 
gram x); Liparytes, quartz-porphyries, pantellarytes (diagram 
xi); Granites, basalts (diag. xii); Gabbros, norytes (diag. xiii 
and xiv) ; phonolytes and eleolitic syenites (diag. xv-xvi); or- 
thophyres; quartz diabases, gabbros, norytes ;camtonytes. mi- 
nettes, kersantytes, mica-diorytes; Tephrytes and leucitytes; 
Tinguaytes. terchenytes and teralytes; Grorudytes; Nordmar- 
kytes; Schlosbergytes; Lindeytes; Malignytes; Missourytes; 
Monsonytes; Schonkinytes; Monchikytes. It is not necessary 
to go into the particulars; further, the author puts great stress 
on a discussion of the opinions of others. Footnotes show the 
authors cited. As to his own opinions on different rocks, the\ 
are pretty much expressed by means of the table of classifica- 
tion given above, and in the curves that represent them. These 
curves are, constructed in the manner of the curves I and II, 
and are found in the first three tables, but in a degree of dis- 
