189] - Mineralogy and Petrography. 851 
portion of the volume are also described andesitic and basaltic g 
which are much more acid than the holocrystalline rocks with which 
they are associated. The basalt glass has the composition of an obsi- 
dian, and passes into a rock with the appearance of basalt, Analyses 
I. and II. are of obsidian and basalt respectively : 
SiO, P,O, TiO, ALO; FeO, FeO MnO NiO CaO MgO 
1 95.40 172 n4 14 1.55 1.26 
11.::57:.37 .02, .00 36.06 $06 446. cae A 44 CUM 
NaO K,O. CL HjO-.Sp Gr. 
8.00. 45 iR — id 2.39 
3.05 1.50 .74 2.83. 
The difference in structure of the two rocks is supposed to be due to 
differences in composition of the original magma,——As an introduc- 
tion to his description of the minerals of the syenite-pegmatite veins 
of Southern Norway, Brégger® gives a short account of the geology 
of the region in which these veins occur, and gives his reasons for re- 
garding the lattter as eruptive in origin, as against the lateral secretion 
theory proposed to account for them. Since the article is itself an 
abstract of a monograph on the geology of the region, it is difficult to 
give a résumé of its contents. Among the rocks discussed are some 
new types, to which reference may be made. Laurvikite is a typical 
augite-syenite composed of anorthoclase (or cryptoperthite) diopside, 
zegerine, and lepidomelane, with small amounts of barkevikite, olivine, 
sphene, magnetite, apatite, zircon, nepheline, cancrinite, and sodalite, 
It is granitic in structure, except on its periphery, where it is developed 
as the well-known rhombic porphyry. This latter occurs also as 
dykes in the former and as flows. A variety of the laurvikite, in which 
oligoclase is present in addition to the anorthoclase, and in which 
sections which characterize if in the laurvikite Brögger calls 
augite-mica-syenite, since it contains very little nepheline. Another 
rock very characteristic of the region is called laurdalite. This is a 
coarse-grained nepheline-syenite, with or without olivine, It contains 
more nepheline and sodalite than does laurvikite, and the former min- 
eral is porphyritically developed. It is the rock described by the 
author as nepheline-syenite® in a former publication. The dyke rock 
corresponding to laurdalite is a nepheline-rhombic-porphyry, which 
differs from the porphyritic laurvikite in containing nepheline in its 
5 Zeits. f. Kryst., etc., XVI., 1890. 
6 Silur, Elagen, 2 and 3, » 273. 
. Nat. — September. — 
