﻿52 NEW YORK STATE MUSEUM 



are obscure as to boundaries or are of too small development to 

 map separately. 



(4) Intcrbedded quart zite. Always a quartzite schist and 

 always exhibiting conformity with the banded gneisses and schists. 

 This is regarded as the uppermost member. 



(5) Fordham gneiss (Banded gneiss). Granitic and quartzose 

 black and white banded gneisses and schists of very complex com- 

 position and structure. 



(6) Interbedded limestones. Crystalline. Interbedded, very 

 impure, serpentinous and tremolitic, granular dolomites, usually 2 

 to 50 feet thick, possibly reaching a thickness of more than 100 

 feet in a few cases. 



(7) Older intrusive gneisses. Variable types, mostly granites or 

 diorites, strongly foliated sills. 



Many are of very obscure relations. The line of close distinction 

 between recrystallized sediment, segregations accompanying that 

 change, and true igneous injection can not be drawn. 



i Special additional igneous types. Under this heading are 

 included the massive or little modified, not at all or only moderately 

 foliated, igneous masses of later origin and local rather than re- 

 gional development. In some cases, however, they are of decidedly 

 controlling importance in the local geology and rise to the status 

 of definite formations. The most noteworthy of these within reach 

 of the aqueduct explorations are : 



(8) The Storm King Mountain gneissoid granite 



(9) The Cat Hill gneissoid granite (central Highlands) 



(10) The Cortlandt series of gabbro-diorites (near Peekskill) 



(11) The Peekskill granite (east of Peekskill) 



(12) The Ravenswood granodiorite (Long Island City) 



(13) The pegmatite dikes and lenses (segregational aqueo- 



igneous type) 



(8) The Storm King gneissoid granite is one of the largest of 

 the clearly igneous and less completely foliated types. It consti- 

 tutes the whole of Storm King mountain and the larger part of 

 Crows Nest on the west side of the Hudson, and, crossing the river, 

 forms the chief rock of Bull hill and Breakneck ridge. It is a 

 rather acid, coarse grained, reddish granite with considerable 

 gneissoid structure in a large way [see Hudson river crossings, 

 pt2]. 



(9) The Cat Hill gneissoid granite is not essentially different 

 from the Storm King type as a physical unit. Its occurrence at a 



