i889j Mineralogy afid Petr-ography. 441 
and tufts of a fibrous titanium mineral.— The alteration of an 
epidiorite into a chlorite schist is described by Hutchings' 
from Tintagel N. Corniwall. The epidiorte contains, in addi- 
tion to the usual constituents of this rock, grains of colorless 
epidote, a little calcite, a very little quartz and some second- 
ary feldspar. As schistosity is induced the amount of calcite, 
chlorite, and quartz increases, and epidote disappears, until 
finally a typical chlorite schist results. — Brief descriptions 
of the rocks of Somali Land, in Northeastern Africa, and of 
the island of Socotra are given by Miss C. A. Raisin= in recent 
numbers of the Geological Magazine. Those of the former lo- 
cality are granites, hornblende, diabases, porphyrites, gneisses, 
and talc and epidote schists, overlain by limestones and other 
sedimentary rocks. On Socotra is a felsite with corroded quartz 
crystals, in which the included groundmass forms concentric 
rings separated by quartz material— Ternier' describes very 
greatly corroded quartz crystals in a micro-granilite from 
Osaka, Japan. These crystals are surrounded by little islands 
of quartz with the same optical orientation as the larger grains, 
and the entire group is enclosed in a zone, composed of fibres 
of quartz and orthoclase, of which the former extinguish par- 
allel to the large quartz crystal. — Wyronboff' has analyzed 
a specimen of the black, opaque, friable obsidian, with a fatty 
lustre, that occurs at Obock, and obtained the following result: 
S:0, A,03 FeA MgO V.O H.O Sp. Gr. 
70.00 13.88 2.77 1.20 7.78 4- 1 1 2.345 
Miscellaneous. — Etched figures. — It is well known that 
the character of the figures produced by etching a crystal of 
quartz with hydrofluoric acid varies with the nature of the 
crystal, and also with the symmetry of the face acted upon. 
With a knowledge of these facts, Messrs. Otto Meyer and 
Penfield have subjecte d a sphere of quartz to the influence of 
strong hydrofluoric acid, and have presented their results in a 
beautifully illustrated article. The difiference in the case with 
which the acid etches various portions of a crystal of quartz is 
finely brought out by the shape which the sphere assumes 
' Geol. Magazine, Feb. 1889, p. 53. 
» Geol. Magazine, 1888, p. 414 and p. 504. 
3 Ball. Soc. Fran?, de Min., xii., p. 10. 
* Bull. Soc. Fran?, d. Min. xii., p. 31- 
« Trans. Connecticut Acad., viii., 1889, p. 158. 
