402 JULIEN 



small part of a grain, sometimes crossed by another set of bands 

 after the pericline law ; the small extinction angle suggests an 

 acid variety. Quartz grains occur in less abundance, with a 

 few inclusions of black particles, colorless needles (perhaps 

 apatite), chlorite scales, and many sheets of fluid cavities with 

 bubbles. The cracks in the larger grains and the groups of 

 angular granules imply partial crushing and granulation. Wavy 

 extinction prevails in both quartz and feldspar. Zoisite appears 

 in colorless, six-sided to rounded granules, with high relief, 

 scattered sparsely through quartz, feldspar and hornblende — 

 as in the diorite-schist of Manhattan Island ^ — but not in saus- 

 suritic form. The ferro-magnesian minerals are also abundant 

 and consist mainly of an orthorhombic pyroxene and three va- 

 rieties of amphibole. The pyroxene, in brownish white fibrous 

 blades, with parallel extinction, shows an absence of dichroism 

 pointing to enstatite, or in other grains di*stinct dichroism, 

 colorless to pale yellow, indicating bronzite, through with rare 

 original inclusions. Hornblende, brownish green to yellow, 

 also occurs as a primary mineral, with strong dichroism and 

 absorption; maximum extinction angle ii°. Still more com- 

 mon is a straw-colored to colorless amphibole, the former feebly 

 dichroic ; maximum extinction angle 8°. The bronzite and 

 both varieties of amphibole occupy the central part of larger 

 grains which pass at the margin, most deeply at the ends of the 

 fibers, into brownish white amphibole (like tremolite), with its 

 fibration always continuous with the cleavage direction of 

 the inner mineral. This fringe of colorless amphibole is invaria- 

 bly coated by thin filmy wisps of bluish green chlorite, in mi- 

 nute scales and blades, which also stretch out here and there 

 along clefts and interstices of adjoining grains of feldspar and 

 quartz. Sometimes a thin seam of brov/n biotite, in minute 

 scales, intervenes between the amphibole and chlorite. The 

 fibration of this amphibole is exceedingly fine, often producing 

 the effect of a milky cloudiness; extinction angle, o° to 5°. 

 It is sometimes filled with black particles of iron oxide and may 

 enclose biotite in elongated scales lying parallel to the fibration. 



'Julien, loc. cit., 436. 



