THIRD HYPOTHESIS OF DERIVATION 



471 



tive evidence on the intersection of gneisses by the hornblende schist, 

 which prevails on Manhattan island. 



There 3^et remains, however, some positive evidence on this point in 

 the apparent survival of apophyses. At the West One hundred and 

 nineteenth street locality a small arm (at A, plate 61), about li feet in 

 length, may be seen projecting from one of the la3^ers of hornblende schist 

 into the adjoining pegmatitic gneiss (figure 1, plate 63) in a fashion 

 which suggests the survival of a sheared apophysis thrust out from a trap- 

 sill. Another is seen close by, between One hundred and seventeenth 

 and One hundred and eighteenth streets ; yet another, about 2 feet wide 



FitiUBE 6. — Tongue of Biotitic Quartz Diorite Schist {end of sheared layer?) in Micaceous Gneiss, with 



adjacent Lenses of Pegmatite. 



In Morningside park, opposite West One hundred and eleventh street. 



in cross-section, is shown in similar position within Morningside park, 

 opposite West One hundred and eleventh street, on east side of ascent of 

 a path, close to the same avenue (figure 6). This, however, may be the 

 sheared extremity of a sheet. 



The street-cutting on west side of the avenue, 100 feet north of One 

 hundred and tenth street, shows similar tongues of biotitic diorite gneiss, 

 1 foot thick below, thrust up between the layers of the micaceous gneiss 

 and tapering off to a thin edge b}^ the side of a sheet of the same diorite 

 schist, 5 feet in width (figure 7). A similar one occurs at the outcrop on 

 the Speedway, at about One hundred and ninety-third street. 



