202 The American Geologist. October, looo 
This texture has been styled "zonary" by Grant*, but in the 
cases observed by the writer, scarcely any zonal arrangement 
can be seen, the various areas being apparently wholly irregu- 
lar in relative position. In the second texture, the same di- 
vision into areas of different orientation is to be observed, but 
no difference of color exists. On the other hand, the cleav- 
ages change more or less in direction in passing from each 
area into another. This texture has been called "polysomatic" 
by Lawsont. The mineral appears as if it had been subjected 
to severe strain at some time, which has twisted the crystal 
without breaking it. At the same time the surrounding 
minerals, which clearly formed before the pyroxene (ophitic 
texture), show yo sign of the least pressure. The explanation 
which the writer would offer is that after the complete forma- 
tion of the labradorite crystals, and after the pyroxene had 
also crystallized, but was, nevertheless, still slightly plastic, 
the rock suffered a strain insufficient to affect the labradorite, 
but sufficient to deform the still plastic pyroxene. An ex- 
ample of such a deformed pyroxene is shown in Plate XVII, 
Fig. 4; it must be repeated that the surrounding feldspar 
crystals are wholly intact. 
The mineral alters commonly to brown hornblende; it 
sometimes alters directly to biotite; oftener it alters first to 
hornblende which in turn produces biotite. It also changes 
to chlorite. 
This pyroxene was isolated in the following manner: the 
minerals of gravity less than 3.31 were first separated out of 
the powdered rock. A weak bar magnet then removed a part 
of the magnetite, and afterward a strong electromagnet re- 
moved considerable more. The remaining powder was then 
digested in warm hydrochloric acid for twelve hours, filtered, 
dried, and again passed through the heavy liquid (3.3), thus 
removing all trace of olivine. Examined with the microscope 
it appeared that the pyroxene was wholly unattacked, but there 
still remained a very appreciable amount of an opaque black- 
mineral having the lustre of magnetite; since it was not at- 
tracted by a strong magnet nor soluble in warm hydrochloric 
*U. S. Grant: The geology of Kekequabic lake: 21st Ann. Rep. 
Geol. Nat. Hist. Surv. Minn. 1893. 
fA. C. Lawson: Notes on some diabase dikes in the Rainy lake re- 
gion: Amer. Geol. I, 1888. 
