1893, ] Mineralogy and Petrography. 383 
the usual heavy liquids and by means of the molten substances sug- ' 
gested by himself’ for this purpose a few years ago, thus obtaining 
mixtures of mineral grains of about the same density. These then 
were studied carefully by comparison of their indices of refraction, by 
immersing them in liquids of known optical densities, until one was 
found in which the grains became almost invisible. The index of 
refraction of these is nearly that of the liquid, consequently their 
nature is thus approximately determined. Microchemical tests and 
the ease with which cleavage laminze were produced, served to distin- 
guish accurately between minerals having nearly the same refractive 
index. The principal minerals identified by the author are ortho- 
clase, quartz, microline, plagioclase, cordierite, calcite, apatite,.amphi- 
bole, tourmaline, pyroxene, epidote, sphene, sillimanite, olivine, gar- 
net, staurolite, disthene, corundum, spinel, rutile, zircon, magnetite and 
ilmenite. The surprising discoveries are those of cordierite, calcite 
and olivine, and of glaucophane among the amphiboles. The propor- 
tions of the various minerals present according to specific gravity was 
2.5% between 2.5 and 2.6; 85% between 2.6 and 2.7; 7.5% between 
2.7 and 3. ; 1.5% between 3 and 3.3; 1% between 3.3 and 3.6; 2.4% 
between 3.6 and 4.2; .1% between 4.2 and 5.2. The sands are sup- 
posed to have come mainly from the rocks of archean terraces. 
Quartz-Gabbro in Maryland.—In the Baltimore gabbro area, 
according to Grant,” are quartz. gabbros consisting of bytownnite, 
quartz, hypersthene, secondary hornblende, and a few accessories. 
The quartz is limpid, and is almost free from inclusions, except for 
lines of small liquid cavities that traverse the grains, as is usual in 
granitic quartz. Diallage, which is so common in the normal gabbro 
` of the region, is entirely absent from the quartz-bearing phases, which 
thus becomes a quartz norite. 
Minerals from the Diamond Fields of Brazil.—Hussak" 
describes the characteristics of crystals of brookite, cassiterite and 
-Xenotime from the diamond region of Dattas, Minas Geraes, Brazil. 
On brookite from the sands of Diamantina was found the new pyramid, 
4P%. The cassiterite is from Manquinho, near Sao Paulo. It occurs 
in a rubellite-bearing lepidolite granite. The zxenotime accompanies 
the brookite in the sands of Dattas. On one doubly terminated crys- 
9Cf., AMER, NATURALIST, 1890, p. 175. 
Johns Hopkins Univ. Circ. No. 103. 
"Min. u. Petrog., Mitth. xii, p. 455. 
