MAGMATIC DIFFERENTIATION OF IGNEOUS ROCKS 349 
EXPLANATION 
No. 30: Spherulitic glass basis from liparites—No. 31: groundmass from 
quartz-porphyry.—-Nos. 32, 33: Glass basis from trachytes.—Nos. 34, 35, 30: 
Glass basis from spherulitic rocks—Nos. 36, 37¢: and C2, 38, and 40: spplucinulittes 
from spherulitic rocks. 
Nos. 30, 32, 34, 35, 30-40 reprinted from the above-cited excellent treatise of 
Lagorio, 1887.—No. 31, see Zirkel’s textbook—No. 33, Williams, Neues 
Jahrb. f. Min., Geol. u. Pal., Beil. eo V, 1887 (see also my treatise in Tscherm. 
Mitt., Vol. XXIV [1905]). 
crystallization. In judging these analyses we must take into 
consideration that throughout a little alkali was probably extracted 
from the glass basis, so that the determined percentages of alkalies 
may bea trifle toolow. The analyses are generally arranged accord- 
ing to decreasing K,O (Or) or increasing Na,O (or Ab+An). 
We especially direct attention to the close accordance between 
these analyses of the residual magmas resulting from the solidifica- 
tion—partly from dike and surface rocks, and partly from deep- 
seated rocks'—and the eutectic Qu:Or:Ab+An, calculated on the 
basis of the graphic-granite analyses and the theoretical explana- 
tions. (See the table, p. 339.) The accordance is especially pro- 
nounced when we take into consideration that the percentage of 
SiO, in the analysis of graphic granite will be reduced about 1 per 
cent when r or 2 per cent of ferromagnesian silicate and magnetite 
is added, and that the analyses of groundmasses, etc., which are 
rich in plagioclase, contain a little more CaO (or An) than the 
graphic granites calculated in the table, page 339, where only a 
small admixture of An is presupposed. The analyses in the 
table, page 348, of the residual magma represent the granitic eutectic, 
consisting of predominant Qu, Or, and Ab+An, with the addition 
of quite small admixtures of iron oxide (Fe,O,) and ferromagnesian 
silicate. 
If we leave the latter quite subordinate admixtures out of . 
consideration, the analyses Nos. 25¢2, 23c, 26c, 36, 37c, and 38 
almost exactly represent the “ternary”? eutectic Qu:Or:Ab 
(or Ab+An) with nearly exactly 0.4 Or:o.6 Ab (or Ab+An). 
And this we may by a short catchword name the “‘ternary”’ granitic 
* Regarding the inconsiderable influence of the pressure on the composition of 
the eutectic we refer to a following chapter. 
