156 PERIDOTITE. 



fibrous material having a feeble polavizatiou and containing irregular brownish-yellow 

 spots, which affect polarized light more than the enclosing material does. The exterior 

 portion of these nodules is formed of pyroxene granules (diallage) somewhat serpentinized 

 with irregular grains of a deep-green color and isotropic, — pleonaste. 



River Oisaiii, Timor. 



Dr. A. Wichmann describes from tlie Eiver Oisain a serpentine of a dark bluish-gray 

 color, porphyritically holding bronzite crystals and small grains of calcite. 



Microscopically the serpentine has the usual mesh structure, and contains within its 

 interstices colorless patches showing aggregate polarization. Opaque grains of iron ore 

 are common. The bronzite is altered, and contains along the cleavage lines a blackish- 

 brown aggregate of minute plates as well as black needles. Chromite in brown trans- 

 lucent grains, and calcite also, were seen,* 



Range 11, Riviere des Plantes, Canada. 



According to Mr. Frank D, Adams, this serpentine contains a few remains of a 

 rhombic pyroxene (enstatite), which are slightly pleochroic and have numerous black 

 needles arranged parallel to the cleavage and rhombic axis.-f* 



Mclhoiirne, Canada. 



According to the preceding observer, this rock is of a dark-green color, and composed 

 of a serpentine mass containing some irregular fragments of a rhombic pyroxene (en- 

 statite). These show pleochroism varying from green to a I'eddish color, and have a 

 well-marked cleavage or fibrous structure.-|- 



Galicia, Spain. 

 The serpentines of this country are composed, according to Macpherson, principally of 

 serpentine produced from the alteration of olivine, and holding the remains of enstatite or 

 diallage crystals, etc.J 



High Bridge, Hunterdon Co., New Jersey. 



1403. A mottled rock of black and oil-green, having a reticulated and somewhat 

 banded structure. Tlie powder of the rock is attracted by the magnet, and tests show 

 the presence of chromium. 



Section : greenish-white with black and dirty-brown spots. The least altered portions 

 are the dark spots, with their included crystal forms. The spots show the structure in 

 common and polarized light of serpentinized olivine, while the crystal forms present a 

 cleavage similar to that of some enstatite, but more like that of diallage. Both spots and 

 crystals are now completely changed to serpentinous material. The main mass of the 

 section is white, slightly tinged in places with a pale yellowish-green color. It is 

 traversed by fissures, and contains much disseminated iron ore in dust, grains, and irreg- 

 ular aggregations. In common light this groundmass shows but little evidence of its 

 origin, but in polarized light there is distinctly revealed the usual network of serpentine 

 fibres when formed from the alteration of an olivine rock. The story of the change can 



* Samml. Gcol, Mas. Leiden, 1881, ii. 105-110. + Aiiiil. Soc. Esp. Hist. Nat., 1S81, x. 50-53. 



t Report ol" Progress; Gcol. Survey of Canada, 1880,-81,-82, p. 19 A. 



