and the Northern part of New York Island. 429 
extensive joint or fracture. The surface over a large area 
‘ looks as if made up of the flat ends of great and nearly hori- 
zontal columns (fig. 26). The rock is here largely hornblendic, 
27, 
quartz, often fail of bedding, and look enough like igneous 
rocks to be frequently referred, without a question, to that class. 
Ihave observed other examples on New York Island, and 
between 133d and 138th streets. The rock over the higher 
rocky portion of the Park, north of the center (as long known) 
is largely hornblende schist, in many parts epidotic. The beds 
are bent in zigzags, and sometimes vary 90° in strike in a few 
micaceous gneiss outcropping on 10th and 11th Avenues vary 
little in strike or dip. Such zigzags, however, although com- 
mon in the hornblendie beds, are not confined to them. 
” i _L. D. Gale respecting hornblende beds 
in aid iin en. pra Bridge (hited in Mather’s N. Y. 
Report, p: 599): “in places hornblende so predominates as to cause the rock to 
assume a columnar structure.” 
