206 ANNALS NEW YORK ACADEMY OF SCIENCES 



undoubtedly a part of the Inwood, that these schists are a part of the 

 Manhattan formation. 



A specimen collected one-half mile southeast of Bedford Village along 

 the road to Stamford, when examined under the microscope in thin sec- 

 tion, shows a medium-grained crystalline texture and foliated structure. 

 The principal minerals present are quartz, feldspar and biotite. Pyrite 

 and magnetite occur in minor amounts. The feldspar consists of both 

 orthoclase and plagioclase, the latter showing extinction angles up to 30° 

 in sections at right angles to the albite lamellae. It is probably an acid 

 labradorite variety. The feldspar and quartz occur in irregular, fairly 

 even-sized, interlocking grains. The biotite occurs oriented parallel to 

 the plane of foliation and shows intense pleochroism from light yellowish 

 to dark reddish brown. Another specimen collected one mile northwest 

 of Poundridge shows very little variation in texture, structure or miner- 

 alogical composition from the above. The plagioclase here shows extinc- 

 tion angles up to 22° 30' and is evidently andesine. A light pink garnet 

 containing numerous inclusions of quartz and biotite is present in con- 

 siderable amounts. 



From the above description it will be seen that the rock is lithologically 

 very similar to certain types of Manhattan schist occurring quite abun- 

 dantly elsewhere. In this schist, however, southeast of Bedford Village, 

 large ^'augen" of feldspar, usually orthoclase, which reach a length of one 

 inch or more at times, are locally quite abundant, so that the rock becomes 

 an "augen" gneiss. A further discussion of these "augen" will be taken 

 up under pegmatitic intrusions in a later paragraph. 



With the exception of the above occurrence of ''^augen" gneiss at Bed- 

 ford Village, the schist does not show any petrographic feature essentially 

 different from those already described from Manhattan Island and the 

 region immediately to the northwest, until an outcrop occurring just 

 north of Croton-on-the-Hudson is reached. Following north from this 

 point along the road to Peekskill one crosses an area of the schist which is 

 less thoroughly metamorphosed than most of the schists of the same age 

 occurring to the south and also than those occurring one and one-half 

 miles further north, in the vicinity of the Cortland intrusions which will 

 be discussed later. * 



Just north of Croton Village, along the above road, the schist has a 

 dark gray color and very foliated structure. In a hand specimen, it ap- 

 pears to be made up largely of prominent crystals of biotite imbedded in 

 a fine shiny matrix consisting mostly of muscovite. Under the micro- 

 scope, the most prominent mineral is seen to be biotite (PL XIII, Fig. 4). 

 It is a deep reddish brown variety showing marked pleochroism and 

 nsiiallv has its basal section oriented parallel to the plane of foliation but 



