FETTKE, MANHATTAN SCHIST OF NEW YORK 241 



spar are occasionally associated with these. In thin section, the matrix 

 in which the feldspar '^augen" are imbedded has a medium-grained crys- 

 talline texture and distinctly foliated structure. Its minerals are quartz, 

 biotite, some feldspar, mostly microcline, and a little plagioclase. Apa- 

 tite occurs as an accessory constituent. Many little veinlets of intro- 

 duced quartz parallel to the foliation are present with which the feldspar 

 "augen" are sometimes associated. These feldspar "augen" consist of 

 orthoclase and microcline and sometimes show a perthitic intergrowth 

 with plagioclase. 



About two miles south of Bedford along an east and west road, there 

 is an interesting outcrop which exhibits a transition from a true pegma- 

 titic sheet parallel to the foliation, into ^^augen" gneiss and finally into 

 mica schist with only a few "augen" of feldspar. Plate XI, Fig. 2, shows 

 a specimen in which prominent "augen" of pink feldspar are developed 

 along little pegmatitic stringers with wliich the schist is thoroughly in- 

 jected. 



About one and one-half miles northeast of North Castle, the "augen'^ 

 structure is developed in a hornblende schist. This is a black more or 

 less foliated rock. In thin section, one observes plagioclase, dark green 

 hornblende with good prismatic cleavage and deep brown biotite. The 

 plagioclase gives extinction angles up to 12° in sections at right angles 

 to the albite lamellae and is therefore oligoclase-andesine. Apatite is an 

 abundant accessory constituent. Magnetite and a little titanite are also 

 present. The "augen" show very much the same characteristics as those 

 already described. They consist of orthoclase and some microcline. in 

 one case, a micrographic intergrowth of orthoclase and quartz was no- 

 ticed. The bands of "augen" gneiss here have very much the same 

 relation to the hornblende schist as the others did to the mica schist. In 

 this case, the matrix in which the "augen" occur consists essentially of 

 the same constituents as the hornblende schist. 



Professors Luquer and Eies,*^ in their study of this "augen" gneiss, 

 came to the conclusion that it represents a metamorphosed igneous rock 

 of the composition of a granite or aplite. The metamorphic action, they 

 thought, produced the gneissoid structure by pressure and a granulation 

 of the minerals, the unsheared portions of the rock remaining as "augen." 



A chemical analysis made by the Avriter of the "augen'^ gneiss described 

 from the outcrop along the road two-thirds of a mile southeast of Bed- 

 ford Village along the road to Stamford gave the following composition : 



*^0p. cit., p. 205. 



