﻿GEOLOGY OF THE NEW YORK CITY AQUEDUCT 



57 



UNCONFORMITY 



Group h Older crystallines (Highlands gneisses) 

 (Grenville series of metamorphics and intrusives — Precambrie) 



(4) Interbedded quartzite. A 



quartzose schist 



(5) Fordham gneiss (chiefly 



sedimentary) . Granitic 

 and quartzose banded 

 gneisses and schists of 

 very complex develop- 

 ment 



(6) Interbedded limestones 



(Grenville) associated 

 with the Fordham 



Gren- 

 ville - 

 Series 



Formations character- 

 istic of the High- 

 lands and some of 

 larger ridges extend- 

 ing southward to 

 New York city. A 

 series, which in petro- 

 graphic variety, is as 

 complex as all of the 

 rest of the forma- 

 tions of the region 

 together 



gneisses 



(7) Old intrusions. Large and varia- "] 



ble masses of granitic gneisses 



of igneous origin cutting the I -, ^ .... 



~ & ... . & . % t y Poster en ville in age 



Grenville series, such as Storm r 



King granite, Cat Hill granite, 



etc. 



Group i Special additional 



(8) Storm King gneissoid granite, 



Storm King-Breakneck district 



(9) Cat Hill gneissoid granite. Garri- 



son district 



( 10) Cortlandt series of gabbro-diorites. 



Peekskill-Croton district 



(11) Peekskill granite. A boss, related 



to the Cortlandt series. Peeks- 

 kill district 



(12) Ravenswood grano-diorite. A 



boss. Brooklyn, Long Island 

 City and Southern Manhattan 



(13) Pegmatites. Dikes, lenses, segre- 



gations of general distribution 



igneous types 

 These are masses of 

 strictly igneous origin 

 (except the pegma- 

 tite) and of larger 

 development which 

 either because of 

 their abundance (peg- 

 matites) or large area 

 (Cortlandt) or eco- 

 nomic features 

 (Peekskill) or im- 

 portant bearing upon 

 the plans of the aque- 

 duct (Storm King) 

 are worthy of sepa- 

 rate note. 



