434 A. A. JULIEN AMPHIBOLE SCHISTS OF MANHATTAN ISLAND 



epidote and apatite occur in some parts, but no calcite was detected by 

 the eye. 



Through variation in-constitution from increase of biotite and addi- 

 tion of pegmatitic material, the schist changes in places into hornblendic 

 gneiss, biotitic hornblende schist, biotite schist, and dark micaceous 

 gneiss, richer in biotite than the contiguous countr}^ rock. 



The following specific gravity determinations have been made on the 

 schist from various localities, using lumps in distilled water at about 20 

 degrees Centigrade : 



Locality. Specific gravity. 



East Forty-third street, between Second and Third ave- 

 nues 3.322 Epidotic. 



East Sixty-ninth street to Seventieth street, near Second 

 avenue 3. 108 



West Seventy -ninth street, subway, in Central park 3.067 



West Ninety-second street and Riverside avenue 3.100 



One hundredth street and Fifth avenue 2.996 Epidotic. 



West One hundred and nineteenth street and Morningside 

 avenue west 3. 270 



Same locality 3.119 Dioritic gneiss. 



West One hundred and thirty-fifth street, near Eleventh 

 avenue . . . , 3. 138 



West One hundred and fortieth street and Seventh avenue. 3.004 



West One hundred and forty-fourth street and Seventh 

 avenue 3.113 



West One hundred and sixty-third street, on Croton aque- 

 duct 3.029 Dioritic gneiss. 



West One hundred -and ninety-eighth street and Fort Wash- 

 ington avenue 3.003 Dioritic gneiss. 



West Two hundred and seventh street and Prescott avenue. 2.965 Dioritic gneiss. 



Same locality (Spuyten Duy vil creek) 3.041 



New Rochelle, Westchester county 3.165 



MICROSCOPIC DESCRIPTION OF HORNBLENDE SCHIST 



In addition to the thin-sections prepared from the schist at West 

 One Hundred and Nineteenth street, mainly considered in the follow- 

 ing description (slides A), others have been examined from nine other 

 localities, namely: 



B. Hornblende schist, West One hundred and twenty-second street and Saint 

 Nicholas avenue. 



C. Biotitic hornblende schist, East Fifty-second street and Madison avenue. 



D. Hornblende schist (street unknown). 



E. Hornblende schist (street unknown). 



F. Quartz-diorite schist, on Speedway, One hundred and eightieth street and 

 Harlem river. 



G. Hornblende schist, Fordhani, near Tremont street. 



