160 General Notes. [February, 
ANDESITE.—The question of the best definition of andesite is 
of plagioclase and hornblende; and Lagorio as a volcanic rock 
composed of plagioclase, with the addition of augite, hornblende 
or mica. Rosenbusch’ separates the mica and amphibole ande- 
sites from the augite andesite. Siemiradski finds that the same 
lava-stream varies in acidity, and that, though hornblende is more 
n r in ve 
silica, while hornblende is eitively lacking. “No indication of 
the regular sequence of separation of augite, hornblende and mica 
with i increasing acidity, as observed by Hague and Iddings,* can 
be detected.” He suggests as the best definition of this class of 
rocks the following: Neutral or acid plagioclase rocks, with at 
least fifty-five per cent of SiO,, with trachytic, basaltic or phono- 
litic habit, consisting of porphyritic andesine, with an iron- -rich 
pyroxene, hornblende or mica in a groundmass, composed essen- 
tially of an acid andesine or oligoclase, and an acid glass (mixture 
of oligoclase on haere and amorphous silica) containing micro- 
scopic pyroxen 
The Borbhyritic hornblende of these Ecuador‘andesites is sur- 
rounded by an opacitic rim and contains inclusions of the ground- 
mass, which, under the microscope, are seen to consist of feldspar 
and augite microlites. Moreover, it is not confined to the most 
acid varieties. Consequently, the author suggests that it may 
have been produced, at great depths, in a magma saturated with 
superheated steam under great pressure, while the augite crystal- 
lized from a dry magma under comparatively little pressure—a 
theory very different from the one usually accepted. 
WILDSCHÖNAU GABBRO.—[IĪn a communication on this subject, 
Cathrein’® calls attention to the article of Hatch, already noticed 
in these notes. He claims that the latter’s hornblende-gabbro 
and amphibolite are chlorite-gabbro and chlorite-schist, and that 
there are no proofs of the close relation which that author sup- 
poses to exist between normal gabbro and serpentine on the one 
hand and amphibolite and epidote rock on the other. 
PETROGRAPHICAL NEws.—F. Becke communicates a few notes 
on the rocks of the lower Austrian Waldviertel. At Marburg 
there occurs a granophyre in veins. It consists of zircon in small 
1 Geologische Reisenotizen aus Ecuador, B. Beil. i 
. * Mikros. Phys. ot Massigen eee 1877. oi tas Sa gen Be 
Andesite des Kaukasu 7: 
x ions rok the cos a rocks of the Great Basin. Amer. Jour. Sci., XXVII, 1884, 
. 162. 
: Miner. und Petrog. Mitth., VII, p. ey 
6 NATURALIST, October, 1885, p P- 992¢ 
7 Min. und Petrog. Mittheilungen, VII, p. 250. 
į 
