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 slight greenish alteration along 

 cracks. 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. Titanite is one of the most 

 characteristic minerals of the rock, and is generally quite 

 abundant. In no instance has it been found Avith ci'ystal 

 boundaries, but forms irregular masses, often (piite 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. 

 "Wliile 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 lamelliB, 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 oft'ords 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, Avith 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 tlie Paciflc Slope, p. 123. 



