Ot ns Soe CA 
1895. ] NEW YORK ACADEMY OF SCIENCES. 81 
rocks, and adds that the serpentine of New York City may have 
had a "similar origin. 
Several years ago the writer was informed by Dr. Merrill that 
there were west of Harrison, Westchester county several out- 
crops of a rock apparently granitic. A subsequent visit to the 
locality showed that there were not only a few isolated out- 
crops, but a large area of the rock, extending from a point 
southwest of Larchmont to about a quarter of a mile north of 
Port Chester, a distance of seven miles. The average width of 
the area is one mile. There is an additional smaller area which 
forms Milton Point, east of Port Chester and Rye. It may be 
a branch of the mair area, but this point could not be determined 
owing to the scarcity of outcrops. Between the two and on the 
western edge of the town of Port Chester is an area of serpen- 
tine, but the latter is not considered in this paper. 
5 The southern, western and northern boundaries of the main 
exposure are uncer tain on account of the mantle of drift, but the 
eastern boundary follows approximately the line of the New 
York, New Haven & Hartford Railroad to Harrison and then 
strikes north. 
Throughout its extent the rock has a pronounced gneissic 
structure, which varies from a more or less massive gneiss in the 
central portion of the area to a mica-schist at many points along 
the border. The former is well seen just northwest of the 
Larchmont station, and the latter west of Mamaroneck, Port 
Chester and at the tip of Milton Point. The strike is N. 40- 
60° W., and the dip 70° S. W. 
Just west of Mamaroneck the section along the road exhibits 
strongly the effects of folding and crushing, with the consequent 
formation of ‘“ Augen” of quartz and of feldspar. 
South of Mamaroneck an isolated outcrop of this rock is cut 
by numerous pegmatite veins, but this was about the only point 
where this fact was observed. 
The minerals forming the gneiss are quartz, plagioclase, bio- 
tite, hornblende, orthoclase and in lesser amounts garnet, titan- 
ite, zircon, apatite, muscovite and microcline. 
Though macroscopically the rock varies as noted above, micro- 
scopically there are no such contrasts observable.* 
Quartz. This forms two-fifths to one-half of the rock. It oc- 
curs in grains and rounded masses, filling the spaces between 
the other minerals. The grains are often cracked and show un- 
*This variation without a corresponding microscopic one has been noted by A. B. 
Some in the Granites of Pike’s Peak, Col. Geol. Soc. of Amer., Baltimore Meeting, 
ec., 1894 
TRANSACTIONS N. Y. ACAD. Scr., Vol. XIV., Sig. 6, April 16, 1895. 
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