568 The American Naturalist. [June, 
those thus produced. The diaschistic rocks form complementary mem- 
bers, such as the minettes and aplites. The complementary form of 
salvsbergite is lindoite, a trachytic aggregate of phenocysts of micro- 
perthite and brown biotite, in a groundmass of quartz, biotite, aegerine 
and various secondary products, among which carbonates play an im- 
portant rôle. 
The laws of differentation in the different parts of the dykes are 
studied through the aid of a large number/of carefully made analyses, 
as well as those governing the differentiation of the dyke masses from 
the boss masses. In all cases it is found that the differentiation con- 
sists in an increase in Fe,O, toward the sides of the dyke, and an in- 
crease of the same constituents in the dyke masses as compared with 
the coroesponding boss material. The original magma is believed to 
have split into two magmas, one of which yielded the laccolite and boss 
material, and the other the substance of the diaschistic dykes. The 
former, in turn, split in the same way into a peripheral and a main 
phase, the former of which gave rise to the aschistic dykes. 
The large number of analyses accompanying the discussion, and the 
careful description on which it is based, supply an excellent basis on 
which the long-desired genetic and philosophical classification of rocks 
may be founded, provided the lines of thought developed by the author 
are found to hold for other regions than those of southern Norway. 
The Massive Rocks of Arran.—A very full account of the 
petrographical features of the massive rocks of the southern half of the 
Island of Arran has been given by Corstorphine’. The rock-types in- 
clude pitchstones, quartz porphyries, normal diabase, quartzitic phases 
of the same rock, olivine-analcite varieties and sahlite diabases, all of 
which occur in sheets or dykes. The pitchstone presents no unusual 
characters. The quartz porphyries include those with a spherulitic 
groundmass and those whose groundmass is crystaline, and among the 
latter are microgranitic and micropegmantic varieties. The quartz- 
bearing diabases are usually in sheets. They contain large macroscopic 
quartzes and feldspars, especially near their contacts with the porphyry; 
and at their contacts with the underlying sandstone they contain large 
fragments of this rock. In the normal biabase both hypersthene and 
biotite occur. The large crystals of quartz and feldspar are regarded 
as foreign components, which have been caught up from the porphyry- 
The olivine analcite diabase is a typical diabase in which zeolites, and 
especially analcites, are abundant. These occupy the interstices be- 
3 Minn. u. Petrog. Mitth., XIV, p. 443. 
