1894. | NEW YORK ACADEMY OF SCIENCES. 163 
intersected by bands and frequently surrounded by a zone of 
augite of like orientation with the main mass, but possessing 
lines of parting tranverse to the cleavage. T he zone and bands 
show a greater tendency toward alteration than does the rest of 
the erystal, and are therefore noticeable on a weathered surface 
of the boulder. 
These large, rounded masses of olivine and augite are imbed- 
ded in a very fine grained matrix or ground mass which consists 
of augite as its main constituent with a basic plagioclase feld- 
spar (labradorite?) in lath-shaped twins with wide angle of ex- 
tinction and larger irregular masses as a very secondary com- 
ponent. The following were noted as accessory constituents : 
olivine in small grains ; magnetite in numerous small crystals ; 
titanic iron (ilmenite) in lnth-shaped crystals, networks and ar- 
borescent forms; pyrite; apatite in the usual needles; brown 
hornblende in lath-shaped crystals, usually associated with the 
augite of the groundmass, but sometimes in the feldspar. The 
alteration products seem to be serpentine, chlorite and calcite. 
The specific gravity of the matrix as determined on three pieces 
was 2.98, 3.11, 3.15, giving an average of 3.07. 
The augite of this groundmass is of the regular basaltic type. 
Its color is brownish violet, showing the presence of titanium 
in its composition. It has distinct pleochroism to brownish 
yellow, and its scheme is, rays || (6) violet, || (a) & (c) yellow. 
The angle of extinction of this alsoisat least 44°. The larger 
crystals have almost complete crystallographic outlines and are 
strongly idiomorphic, though they are not strictly phenocrysts, 
as occasionally a small cr ystal of the same indents one. All the 
augite is idiomorphic with reference to the feldspar. 
The larger crystals and areas contain inclusions of undeter- 
mined character and spots which may have been glass originally, 
but now are considerably altered. Around many of the large 
masses of pale green augite there is a more or less complete 
zone of violet augite arranged in minute crystals in parallel po- 
sition to each other, but not to the pale augite. These crystals 
are sharply bounded toward the groundmass, but not toward 
the crystal on which they occur. 
The other constituents of the rock do not demand further 
mention than what is given in the list above. The amount of 
glass present seems to be very small and has been largely, if not 
entirely, devitrified. 
The rock would be classed as an olivine basalt, very poor in 
in feldspar, and therefore inclining toward the limburgite divi- 
sion of the family. 
Am. Mus. Nat. Hist., New York City, March 19, 1894. 
