208 ANNALS NEW YORK ACADEMY OF SCIENCES 



filled with inclusions of nitile needles. Garnet is not as abundant, but it 

 occurs in somewhat larger grains. 



Farther north, an area of schist and limestone undoubtedly belonging 

 to the Manhattan-Inwood series adjoins the Cortland intrusives on the 

 w(>st at Verplanck. The schist here has a medium to fine crystalline tex- 

 ture and a banded rather gneissoid appearance. In thin section under 

 the microscope, it is seen to consist largely of mica, mostly biotite, al- 

 though considerable amounts of muscovite, feldspar and quartz (PI. XIII, 

 Fig- 3) are also present. Minor amounts of a dark brown tourmaline 

 also occur. The biotite shows intense pleochroism from light yellowish 

 brown to deep brown. The feldspar is mostly microcline, which is present 

 in large amounts. The structure is distinctly foliated, due to the parallel 

 oiientation of the mica and the elongation of the feldspar and quartz 

 grains. 



Another specimen of mica schist which occurs interbedded with the 

 limestone at Verplanck, when examined under the microscope, proves to 

 be much less thoroughly recrystallized and metamorphosed than the above. 

 Abundant irregular flakes of deep brown biotite occur in a very fine- 

 grained matrix consisting mostly of quartz and sericite. 



The schist again appears just north of the Cortlandt intrusive rocks. 

 Not far from the actual contact near the southeastern corner of the town 

 of Peekskill, several outcrops occur along the road to Yorktown Heights. 

 The rock is medium to fine grained in texture and distinctly foliated. 

 Under the microscope, it is seen to be made up largely of biotite, sericite 

 and quartz. The quartz grains occurring between the parallel mica flakes 

 are extremely fine in texture. Another specimen taken from a point 

 nearer to the actual contact is much more ciTstalline in its nature and 

 shows a higher degree of metamorphism. Tlie minerals present are bio- 

 tite, muscovite, quartz, feldspar, staurolite, garnet and a little sillimanite. 

 Some dark brown intensely pleochroic tourmaline w^as also noticed. 



North of this area, no further outcrops of true schists belonging to the 

 Manhattan formation occur, but along the northwestern side of the 

 Peekskill Creek Valley about two miles northeast of Peekskill a phyllite 

 appears. A description of this phyllite and a discussion of its relation to 

 the Manhattan formation will be taken up in a later paragraph. 



East and southeast of Peekskill the schists representing the Manhattan 

 formation become coarsely crystalline again and are more nearly like those 

 occurring on Manhattan Island. In places a quartzitic variety predomi- 

 nates. This is made up largely of quartz, with some feldspar, biotite and 

 muscovite and a little garnet. Some magnetite is also present. The 

 quartz and feldspar occur in irregular interlocking grains, while the micas 

 are oriented parallel to the foliation. Both orthoclase and plagioclase are 



