3^4 NEW YORK STATE MUSEUM 



thick and the largest yet seen need not be more than 30 feet. 

 The quartzites and quartz schists are similar in their distri- 

 bution but more common and occasionally more extensive. The 

 banded gneisses and the more massive granitic gneisses are 

 much more heavily developed and their thickness is not known. 



The whole series is folded, crumpled, faulted, crushed, injected, 

 intruded and intensely modified by recrystallization ; but through 

 it all they retain the fundamental association and essential char- 

 acter of an original sedimentary series. Nowhere is there a 

 basal conglomerate. What is beneath is unknown. 



Many of the occurrences of gneisses, a few of the schists, 

 and all of the granites, diorites and gabbros are of igneous 

 origin but all occur as intrusions or injections, as sills, dikes 

 or bosses cutting the metamorphosed sedimentary members of 

 the formation. Except in rare instances they are not even of 

 sufficient constancy or prominence or areal extent or individu- 

 ality to be given an independent designation. The most notable 

 ones coming within such limitations are the " Yonkers gneiss," 

 which appears to have been a great granite sill that can now 

 be traced along the axis of the southern ridges for a distance 

 of 15 miles; the "Storm King granite," which has a large 

 development in Storm King and Crows Nest mountains and 

 in the Breakneck ridge along the northern border of the High- 

 lands ; and the " Cortlandt series " of gabbro-diorite-granite rocks 

 forming an immense boss on the east side of the Hudson river 

 between Peekskill and the Croton valley. Even these, except 

 the " Cortlandt series " are but large, intruded masses wholly 

 within the gneiss formation. At the extreme southeast the 

 " Harrison diorite " in its relations is somewhat similar to the 

 Cortlandt series. Both cut through the gneisses into higher 

 formations. 



That this is the true relation between the igneous and sedi- 

 mentary members is supported by the numerous eruptive con- 

 tacts and inclusion phenomena. Of these no more convincing 

 evidence need be sought than the -occurrence of large angular 

 masses of the banded gneisses and related sedimentary beds 

 of various types wholly included within the granites along such 

 marginal belts as at Constitution island, or on the west side 

 of the Hudson near Fort Montgomery, or at the fresh workings 

 of the Mohegan quarries a few miles east of Peekskill. At 

 Constitution island only the more massive banded gneisses 



