534 THESE VOGAs 
Ann., Vol. CXLI.—Nos. 58a, 6, and c: Philipp, Neues Jahrb. f. Min., etc., 
1871, and Rammelsberg, Pogg. Ann., Vol. CXLI.—Nos. 50a, 5, and c: Bauer, 
Neues Jahrb. f. Min., etc., 1891, II1.—Nos. 60a and b: Knop, Neues Jahrb. f. 
Min., etc., 1877.—Nos. 61a and 6: Linck, Zettschr. f. Kryst. u. Min., Vol. XVIII. 
The value of FeO in the bronzite should be reduced a little 
throughout, probably about one-tenth in most cases. 
Joh. Schiller has discussed the question in hand in a special 
treatise,t partly on the basis of several of the analyses here 
given of olivine nodules in basalts, and partly on the determi- 
nation of the chemical composition of the two minerals on the 
basis of the axial angle and optical character. He comes to the 
result that MgO and FeO in the feldspar-free rocks are quite 
evenly distributed in the olivine and orthorhombic pyroxene, and 
this conclusion is confirmed by my own investigations. But with 
regard to the rocks containing feldspar he supposes a relative, 
sometimes even a relatively extensive, enrichment of MgO in the 
olivine. The observations on which he bases this last construc- 
tion, however, are few, and in my opinion rather dubious.” 
Olivine and orthopyroxene,’ isolated from a series of peridotites 
poor in iron (saxonites, olivine-schists, etc.) with only very little 
Al,O,, Fe.0;, and CaO, show: 
Olivine, 1 MgO:0.08, 0.08, 0.08, 0.10, 0.11 FeO; 
Orthopyroxene, 1 MgO:0.07, 0.07,.0.07, 0.10, 0.12, 0.12, FeO. 
In peridotites, a little richer in iron, and at the same time carrying 
somewhat more Al,O,, Fe,O,, and CaO, we find: 
Olivine, 1 MgO:0.15, 0. 21 FeO; 
Orthopyroxene, 1 MgO:0.13, 0.15, 0.16 FeO. 
As well with. regard to the short report above as to Schiller’s 
investigations, MgO and FeO in the feldspar-free rocks in question 
are quite evenly divided between the two minerals. The various 
lesser differences—which would indicate a small relative enrichment 
1 Tscherm. Mitt., Vol. XXIV (1905). 
2 Especially for the extremely low FeO-contents in olivine from an olivine-gabbro 
from Tilai, Ural. 
3 Enstatite-bronzite-hypersthene deserves, in the same manner as anorthite- 
bytownite-labradorite-andesine-oligoclase-albite, a common term, and as such I will 
use “orthopyroxene,” that is to say, pyroxene belonging to the orthorhombic system. 
I believe I occasionally have heard or read this term before, so the proposition is 
not originally mine. 
