GEOLOGY OP THE NEW YORK CITY AQUElDUC'T 



57 



(5) 



UNCONFORMITY 



Group h Older crystallines (Highlands gneisses) 



(Grenville series of metamorphics and mtrusives — Precambric) 

 (4) Interbedded quartzite. A ] ( 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 



(6) 



Iniiestones 

 ated ! 



Gren- 

 ville < 

 Series 



A 

 quartzose schist 

 Fordham gneiss (chiefly 

 sedimentary). Granitic 

 and quartzose banded 

 gneisses and schists of 

 very complex develop- 

 ment 

 Interbedded 

 (Grenville) 

 with the 

 gneisses 



(7) Old intrusions. Large and varia- 

 ble masses of granitic gneisses 

 of igneous origin cutting the 

 Grenville series, such as Storm 

 King granite, Cat Hill granite, 

 etc. 



associ 

 Fordham 



Postgrenville in age 



Group i Special additional 



Storm King gneissoid granite, 

 Storm King-Breakneck district 



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 



(8) 

 (9) 



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. 



