484 A. A. .TULIEN — AMPHIBOLE SCHISTS OF ^[AXHATTAX ISLAND 



The correspondence of this schist to those already described on Man- 

 hattan island suggests a similar metamorphic histor}''. 



Chloritic and ophiolitic amphibolites. — The gray chloritic amphibolite 

 (New Rochelle) is a coarse variety, with allotriomorphic prismatic grains 

 of dull, greenish gray amphibole, 1 to 3 centimeters long, lying in all 

 positions ; by weathering these become fawn-colored and look like tremo- 

 lite. Chlorite, in dark green scales, sometimes with talc, forms shining 

 films on cleavage planes of the amphibole. Much grayish feldspar (and 

 a little quartz?) occupies the interspaces. 



A similar mottled and coarse amphibolite at Rye shows also abundant 

 flakes and grains of white marmolite and yellow serpentine. 



A somewhat finer grained variety is represented b}^ chloritic tremo- 

 litic diorite or amphibolite. It is a rather coarse rock, consisting chiefly 

 of black hornblende, passing into brownish gray tremolite,up to 1 centi- 

 meter in length, lying in all positions ; much plagioclase, snow white to 

 grayish yellow, in the interstices; shining scales of blackish green chlo- 

 rite abundant, 5 millimeters or more across, often spotted with whitish 

 films (marmolite?). 



A finer grained amphibolite is common at R3^e, dark green, wdth actino- 

 lite needles not exceeding 3 millimeters in length. Others are of a lighter 

 grayish green, glistening wdth minute scales of talc and chlorite, inter- 

 mixed with larger flakes of marmolite or sometimes abundant white 

 calcite. 



The ophiolitic amphibolite (New Rochelle) difi'ers in the general altera- 

 tion of the long hornblende prisms to a browmish gray amphibole or 

 tremolite, accompanied by a large amount of intervening blackish green 

 groundmass, consisting apparently of amphibole, chlorite, and serpen- 

 tine. Some thin segregated seams of white marmolite occur here and 

 there. 



In the thin-sections, under the microscope, deep green spinel, black 

 iron ores, and some brownish iron oxide are distinguished. 



Of serpentine (New Rochelle), there are several varieties, for whose 

 description it is sufficient for m}'' present purpose to refer to the papers 

 of Dana, Merrill, and others. 



An examination of this interesting series from the region northeast 

 of our island has thus shown all transitions from coarse intrusive rocks, 

 evidently nearly related to the quartz diorite of the Harrison tract, but 

 more basic, through metamorphic forms in which the hornblende shows 

 all stages of alteration toward actinolite, and, b}^ shearing, into dioritic 

 and hornblende gneisses and schists which closely approximate, though 

 perhaps they do not quite reach, the extreme degree of crushing and 

 condensation found in manv hornblende schists of Manhattan island. 



