444 A. A. .TTTLTEN — AMPHIBOLE SCHISTS OB' MANHATTAN ISLAND 



street on the East river; West Eighty -fifth street, just east of Tenth 

 avenue ; East Ninety-ninth and One hundredth streets, between Lexing- 

 ton and Fourth avenues; West One hundred and eighth street and 

 Riverside avenue; West One hundred and twenty-seventh street, near 

 Saint Nicholas avenue ; West One hundred and sixty-fifth street, on path 

 above the Speedway ; West One hundred and ninetieth street and Am- 

 sterdam aveuue. 



Through its great plasticity this biotitic or micaceous gneiss often bends 

 about and incloses the bunches of less altered hornblende gneiss in a 

 manner somewhat resembling a flow structure. Prominent localities were 

 noted at West Ninetieth street, between Eleventh and Twelfth avenues ; 

 West Ninety-second street, near the Hudson river ; West One hundred 

 and forty-first street and Seventh avenue. At West Fifty-eighth street, 

 between Ninth and Tenth avenues, a group occurred of four thin layers 

 of slaty hornblende gneiss and one of black biotite gneiss, separated b}^ 

 la3^ers of micaceous gneiss. At Fifty-seventh street, only 200 feet farther 

 south along the strike, this entire group was represented by a single 

 thick bed of black biotitic gneiss. 



DEVELOPMENT OF EPIDOTE, CALCITE, AND SECONDARY HORNBLENDE 



The former outcrop of hornblende gneiss at East Ninety-ninth street, 

 between Fourth and Lexington avenues, was most instructive for study 

 of the following phases: 



(1) General distortion and crumpling of layers ; their close intercala- 

 tion with seams of granite or pegmatite and common intersection by 

 seams or veins of white quartz carrying tourmaline and garnet. 



(2) Passage into black biotitic gneiss, penetrated by hornblende blades, 

 and in places into micaceous gneiss, with many long bladed scales of 

 both black and white micas. 



(3) Epidotic alteration of thin layers, with development of secondary 

 hornblende in brilliant, jet-black plates and aggregates, some prisms 

 reaching 2 to 5 centimeters in length. Scattered scales of biotite, some- 

 times chlorite, represented apparentl}^ the destination of alumina from 

 feldspar and aluminous hornblende during production of epidote. 

 Many minute, pale green blades were assigned to secondary actinolite. 

 Seams of epidosite, bright greenish yellow and finely granular, have 

 been thus formed, up to 8 centimeters in thickness. These are quartz- 

 ose and have been evidentl}^ less plastic than those purely hornblendic. 

 They showed their rigidity and brittleness by frequent fracture into 

 isolated green bunches, still lying in line, often coated by black, second- 

 ary hornblende, penetrated by veinlets of albite and quartz, with lateral 



