HIE SBA SIC NU AUS SH IZ IROCIKS , SB ING. 5 
Flypersthemc Varieties —Closely related to the olivinitic-granu- 
litic gabbros are the hypersthene-bearing varieties. In some 
cases these contain a small quantity of olivine, but in most cases 
hypersthene has entirely replaced this mineral. A few grains of 
the usual colorless olivine, for instance, may be detected on one 
edge of the section of rock No. M. 1347, whereas elsewhere in 
the slide it is lacking. The main portion of the rock consists of 
more or less rounded grains of hypersthene and diallage, and 
irregular masses of magnetite, imbedded in a plexus of irregular 
but nearly equidimensional grains of plagioclase. Magnetite 
particles are included within all the rock’s constituents, and, since 
these are very fresh, the magnetite is probably a separation from 
the magna. The mineral also occurs on the edges of the few 
olivine grains present, but here it is in long stringers that are 
evidently secondary. 
In the great majority of the hypersthene varieties of the 
granulitic gabbros no trace of olivine may be detected either in 
the fresh or in the altered state. Their components are usually 
hypersthene, diallage, feldspar and magnetite. All are fresh, 
except in very rare cases when the feldspar shows traces of decom- 
position. The proportions of the pyroxenes vary widely in dif- 
ferent specimens, even to the complete exclusion of one or the 
other of the two varieties. The purely hypersthenic phases are 
treated with the other hypersthene bearing rocks in this place, 
while the purely diallagic kinds are reserved for later discussion. 
The hypersthene, the characteristic component of these rocks, 
is remarkably fresh and transparent. It is pleochroic in the 
usual light green and pinkish tints, and is often so compact 
that but few cleavage cracks are to be seen in its grains. An 
analysis by Dr. E. A. Schneider of a very pure powder of the 
mineral separated from rock No. 7036, one of the best examples 
of the type without diallage, gave: 
SiON Ol ke On Py heOm) NnOl) CaO, Mic@r EE@r(os5,) Potal: 
48.44 7.91 BR 6 AOS SO NAAM TONS 4508 97-35 
*TiOz was not determined gravimetrically. A colorimetric test showed about .40 
per cent. of this oxide present. 
