472 



A. A. JULIEN — AMPHIBOLE SCHISTS OF MANHATTAN ISLAND 



In addition to these isolated projections of tongues of schist, there ob- 

 tains a common gathering of thin layers in small groups, separated by a 

 few feet or inches of gneiss, which looks like the result of shearing of a 

 series of apophyses of a dike. Thus in the fine exposure of 3 layers of 

 the hornblende schist on the bank of the East river from Sixty-fourth to 

 Sixty-eighth street, one mass, 4 feet thick, in passing a few rods north- 

 ward becomes split up into 8 or 9 thin sheets. This grouping of several 

 separate layers needs, however, to be distinguished from instances of 

 cross-section of several sharp folds in a single layer (West One hundred 

 and tenth Street group), where a more uniform thickness tends to prevail. 



Figure 7. — Emergence of Apophyses and Section of Sheets of biotitic Quartz-diorite Schist. 

 Locality, Morningside avenue west, north of One hundred and tenth street. 



and also from mere alteration of certain bands in a thick layer of horn- 

 blende schist into biotitic gneiss. The following are examples of such 

 clusters of parallel layers in close approximation, those marked ^ being 

 no longer accessible to examination : 



4 layers at West Fifty-eighth street between Ninth and Tenth avenues (*) ; 

 4 to 11 layers at East Sixty-fourth street, on bank of East river ; 



3 layers, 1 to oi feet thick, in the subway through Central park at West Seventy- 

 ninth street; 



4 layers at East Eighty-ninth street and Third avenue (*) ; 



3 layers at East Ninety-sixth street between Fourth and Madison avenues (*) ; 



9 layers at West One hundred and tenth street and Morningside avenue west; 



9 la3'ers, at least, at West One hundred and seventeenth to One hundred and 

 nineteenth street and the same avenue : 



3 layers at West One Imndred and sixty-third street, on the Croton aqueduct ; 

 10 layers at West One hundred and sixty-fifth street, on path above the Speed- 

 way ; 



5 layers at west end of Highbridge, One hundred and seventy-fifth street ; 



