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1886.] Mineralogy and Petrography. 375 
rocks. These are placed vertically in groups, according as their 
cross-sections are isotropic, or show parallel or inclined extinc- 
tion. These groups are again subdivided in accordance with the 
crystallographic systems. Opposite the name of each mineral are 
placed its chemical composition, specific gravity, characteristic 
cleavages, the ordinary forms of its cross-sections, its twinning 
laws, the character and strength of its double refraction, its colors 
under crossed nicols, its natural color and pleochroism, its struc- 
ture, the minerals with which it is generally associated, its char- 
acteristic inclusions and decomposition products, and those pecu- 
liarities which distinguish it from other minerals of the same 
general appearance. In this part an immense amount of material 
is so arranged that with very little trouble the student can turn to 
the mineral whose properties he wishes to study, and find in a few 
brief sentences the characteristics by which it can be distinguished 
from all others. This part will prove of considerable use to all 
who are beginning the study of petrography, and whom such 
manuals as that of Rosenbusch would tend only to confuse and 
discourage. A great service has been rendered to all those to 
whom the material in Dr. Hussak’s book is inaccessible on 
- account of the language in which it is written, and the translator 
deserves the thanks of all those interested in petrography for 
having placed within the reach of American students the elements 
of a branch of geology which is just beginning to be appreciated 
on this side of the Atlantic, as affording a key for the solution of 
many questions which have heretofore been considered as beyond 
the power of penetration. ' 
PeTROGRAPHICAL News.—The relations of the bastite serpentine 
to the troktolite in the Belhelvie parish, in Aberdeenshire, are 
studied by Bonney, and the results of his investigations pub- 
lished in the Geological Magazine! The serpentine is derived 
reactionary rim. The sequence of the two rocks in respect to 
*S¢ Is not satisfactorily decided. In the same paper, the “ Black 
Dog” roc , first mentioned by Heddle? as a mass of rock about 
four y ards long and broad, which projects from the sand on the 
: I ore, is described as containing fibrolite, iolite, quartz and mica. 
t bears a very close resemblance to some of the cordierite gneisses — 
Varia Kiich describes’ a quartz-pyroxene-andesite from 
€ Cumbal in the Andes, in which the pyroxene constituent IS 
Principally hypersthene, and remarks that this mineral is a much 
1 oe 
Me’ $ 439. 
3 : agazine, V, p. I. 
Neues Jahrb, fiir Min,, etc., 1886, I, pe 35- 
$ 
