220 ANNALS NEW YORK ACADEMY OF SCIENCES 



The biotite is a deep brown variety with a slight tinge of red. It occurs 

 sparingly throughout the mass between the tremolite crystals and is also 

 concentrated in lenticular bunches averaging about .2 x .3 x 1.00 inch in 

 size. The talc occurs in tabular flakes among the tremolite crystals. In 

 portions of the sheet, the talc predominates and the rock grades into a 

 talc schist. Veins of asbestiform amphibole up to two inches in width 

 have also been developed in places. This amphibole occurs with its long 

 axis at right angles to the foliation. The tremolite occurs in parallel 

 orientation with the schistosity. The whole mass shows evidence of hav- 

 ing undergone intense shearing accompanied by recrystallization of the 

 constituent minerals into new combinations. 



The mass of actinolite and tremolite schist formerly exposed at Eleventh 

 Avenue and West 59th Street^^ is another example of this type. Here 

 talcose and chloritic varieties, together with serpentine and ophicalcite, 

 were also present in close association with the actinolitic and tremolitic 

 varieties. 



Harrison Granodiorite Gneiss 



Another rock probably quite closely related genetically to the horn- 

 blende schist described is a granodiorite gneiss occurring in the south- 

 eastern portion of Westchester County. Its relation to the mica schist is 

 somewhat similar to that of the hornblende schist, only it occurs in a 

 much more extensive mass. The strike of the gneissoid to schistose struc- 

 ture developed in it is parallel to the foliation of the mica schist adjoin- 

 ing it. 



This gneiss is most extensively developed just across the State line in 

 Connecticut, where it occupies a large area. Two prongs from this mass 

 extend southwest into Westchester County, New York. The northwestern 

 one of these is about one and one-quarter miles wide and extends as far 

 as Larchmont, while the southeastern one is about one mile wide and ex- 

 tends to Eye Point. An area of schist about one and three-quarter miles 

 wide separated the two prongs. 



Professor Heinrich Eies^^ was the first to describe this gneiss from the 

 vicinity of Harrison in Westchester County, and it has since then been 

 generally referred to as the "Harrison granodiorite." The Connecticut 

 Survey^^ on their preliminary geological map of the State, however, have 

 called it the Danbury granodiorite gneiss, correlating it with similar 

 gneisses which are quite extensively developed in other portions of west- 

 em Connecticut. 



2» A. A. JuLiRV : "Amphibole schists of Manhattan Island." r>ull. Oeol. Soc. Am., Vol. 

 14, pp. 421-494. 190.'?. 



^ "On a granodiorito near Harrison. Westchester County, N. Y." Trans. N. Y. Acad. 

 Scl., Vol. 14, pp. 80-80. 1895. 



31 Oeol. and Nat. Hist. Surv. Conn., Bull. No. 7. 1907. 



