MAGMATIC DIFFERENTIATION OF IGNEOUS ROCKS 341 
EXPLANATION 
Nos. 14 and 15: H. Emmons, “Island of Capraja, at Elba,”’ Quart. Jour. 
London, 1893. ‘The two feldspars 14) and 150 isolated by density 2.67—No. 
16: A. Hague and J. P. Iddings, “Volcanoes of Northern California, Oregon, 
and Washington Territory,” Amer. Jour. Sc., 3, Vol. XXVI (1883). Hyper- 
sthene-andesite.—No. 17: A. Lagorio, ‘‘Uber die Natur der Glasbasis sowie 
der Krystallisationsvorgainge in eruptiven Magma,” Tscherm. min. u. petrogr. 
Mitt, Vol. VIII (1887); from Hliniker Valley, Hungary.—No. 18: Hague and 
Iddings (loc. cit.); California. The plagioclase is andesine-oligoclase. The 
determination of SiO, in the plagioclase is too high, owing to impurity.— 
No. 19: Lagorio (Joc cit.). Spherulitic rock; from Alausi, Ecuador.—No. 20: 
Lagorio (Joc. cit.); from Summit County, Colorado. With phenocrysts of 
quartz and two feldspars, one monocline (analysis No. 200) and the other 
tricline—No. 21: Laspeyres (see Zirkel’s Textbook of Petrography, 1894, Vol. 
II, p. 177); from Halle, Germany.—No. 22: A. Streng, Neuer Jahrb. f. Min., 
Geol. u. Pal., 1860, from the Harz Mountains. 
In order to establish that the crystallization in the eruptive 
magmas of the different feldspars and of quartz is in conformity 
with the physicochemical details which we here have developed 
essentially on the basis of the analysis of graphic granite, we refer 
inter alia to my earlier statement in Tscherm. Mitt., Vol. XXV 
(1906). 
On pages 340 and 342 we give a small selection (analyses Nos. 
14-29) from the numerous analyses, compiled from the literature, 
partly of porphyritic rocks, with special analyses of (a) the whole 
rock, (6) the porphyritic feldspar, and (c) the glass or ground- 
mass, and partly of some granites with special analyses of (6) the 
basic concretions (or orbicules), and (c) the inclosing rock. 
Granites with basic concretions (Nos. 24-260), or basic orbs 
(Nos. 276-29b) are shown in Table VI on p. 342. | 
We call special attention to the following: 
1. In the intermediate and the acid eruptive rocks, which 
contain the ordinary admixture of ferromagnesian silicates and 
iron, or titanic iron, ore (especially magnetite and ilmenite), an 
essential part of these minerals crystallizes at an early stage. A 
small quantity of Fe.O,, FeO, and MgO, however, is left in the 
remaining magma. ‘This appears in the solidified rocks as the 
glass basis or groundmass in the porphyritic rocks, or as the inter- 
vening mass between basic concretions or orbicules in granites. 
