.SCHISTS OF WESTCHESTEl?. COUNTY 483 



eiice colors sky blue of second order in the rather thick section ; vague 

 axial figures. A little epidote, in pale yellowish granules, with feeble 

 pleochroism ; inclosed in the feldspar, sometimes in the quartz. 



In the hand specimen this rock differs decidedly in texture and in pro- 

 portion of feldspar from the hornblende gneiss of Manhattan island; 

 but the closer inspection detailed in the above description shows a re- 

 markable resemblance, almost identity, in mineral components and in 

 their optical characteristics. 



There is a hornblende gneiss at Larchmont Manor identical with 

 the hornblende gneiss in parts of the hornblendic outcrop at our locality 

 in West One hundred and nineteenth street. The scales and blades of 

 black hornblende are mostly less than 1 millimeter long. 



This gneiss is commonly distributed near New Rochelle and through- 

 out Westchester county, often passing into black hornblende schist 

 identical in appearance with that of Manhattan island. 



Metamorphic diorites. — The fine-grained quartz diorite (New Rochelle) 

 is a dark green compact and finer grained variety, with granules of 

 amphibole, in part greenish like actinolite, rarely reaching 1 or '2 milli- 

 meters across. The amount of feldspar and quartz in the interstices is 

 nearly equal to that of the hornblende. With increase of actinolite we 

 find the next varieties. 



The blackish green amphibolite (New Rochelle) is a dense, heavy 

 rock, made up chiefly of a very fine groundmass, shot through in all 

 directions by slender blades of black hornblende, 2 to 6 centimeters in 

 length and about 2 millimeters in breadth. The groundmass exhibits 

 under the pocket lens minute scales of dark green amphibole or actino- 

 lite and black mica with grayish particles (probably quartz and feld- 

 spar). A few nests here and there of finely saccharoidal white quartz, 

 up to 3 centimeters in length, show rare facets of white feldspar, and 

 are penetrated in every direction by well crystallized blades of horn- 

 blende showing the prism faces and pinacoids sharply defined. 



The banded epidotic diorite (New Rochelle) is a blackish green rock, 

 rich in slender actinolite blades, with much quartz, a little feldspar, 

 epidote, black mica, and rarely garnet. There is also a finer grained 

 variety. 



Nearly all the hornblende of the actinolite diorite (New Rochelle) has 

 passed into the dark green actinolitic form, intermixed with epidote. 

 White plagioclase is present in large amount, with some grayish quartz. 



'J'he dark green actinolitic schist (New Rochelle) resembles the first 

 form, with the green amphibole predominating in slender needles up to 

 2 millimeters in length, producing a silky luster. In some specimens 

 nests occur rich in white feldspar, up to 2.5 centimeters in length. 



