1893. ] NEW YORK ACADEMY OF SCIENCES. 215 
figured by Becker.* The pyroxene is in irregular, often 
rounded masses, colorless or with a very faint greenish tinge, 
and extinction angle of about 40°. As a rule it is very fresh, 
though sometimes showing a sligit greenish alteration along 
eracks. In one section considerable uralite has formed from it. 
The mica is rather light colored, but strongly pleochroic, and 
always very fresh. It increases in quantity as pyroxene 
decreases, producing phases of the rock that have nearly the 
composition of ordinary gneiss. Tuitanite is one of the most 
characteristic minerals of the rock, and is generally quite 
abundant. In no instance has it been found with crystal 
boundaries, but forms irregular masses, often quite large, and 
is distinctly pleochroic, changing from yellowish to brownish 
red. Graphite occurs in irregular scales, which are usually 
destroyed in the process of section grinding. In the micaceous 
variety of the rock, rutile appears in minute prismatic forms, 
very perfectly developed, and of a redish brown or blue color. 
The characteristic knee-formed twine is occasionally present. 
While in the mass, the rock is prominently schistose, indi- 
vidual layers are often quite massive, and sections from these 
have granitic structure. Other sections show the constituents 
arranged in very distinct layers. Evidences of mountain- 
making action, such as undulatory extinction, bending of 
twinning lamelle, and crushing of minerals, are abundant. 
SCAPOLITE ROCKS. 
One section of the pyroxene rock shows, instead of feldspar, 
some muscovite and a colorless mineral in small plates, with 
somewhat fibrous appearance, which proves to be scapolite. 
This specimen offords a connecting link between the pyroxene 
rocks and another rock rather closely resembling them. It shows 
under the microscope the same pyroxene, mica, titanite and 
pyrrhotite as irregular grains in a paste or ground mass of 
scapolite. This mineral is in large colorless plates, with distinct 
cleavage, which in basal sections shows cracks intersecting at 
right angles. Such sections are dark with crossed nicols and 
give an interference cross, from which the negative character 
of the mineral may be determined. Vertical sections yield 
brilliant interference colors. 
The presence of scapolite in the section of pyroxene rock, seem- 
ingly in the place of feldspar, renders it probable that, as is so 
* Becker, G. F., Geol. of Quicksilver Deposits of the Pacific Slope, p. 123, 
