FETTKE, MANHATTAN SCHIST OF NEW YORK 255 



A quartz diorite was found occurrintr at one place in the schist north 

 of the Highlands which had practically the same relationship to the latter 

 that the hornblende schist has to the Manhattan schist south of the 

 Highlands. 



The folding of the formations north of the Highlands was also accom- 

 panied in eastern Dutchess County and western Connecticut, where the 

 folding was severest, by the intrusion of granites and pegmatites similar 

 to those south of the Highlands. Those who hold that the two series are 

 equivalent believe that the orogenic movements which brought about the 

 folding and metamorphism south of the Highlands were also part of the 

 Green Mountain uplift which occurred toward the close of Ordovician 

 time and brought about the metamorphism north of the Highlands. The 

 axes of the folds in the two regions run in the same general direction. 



The occurrence of an area of phyllite south of the Highlands northeast 

 of Peekskill has been cited as evidence in favor of the Ordovician age of 

 the Manhattan schist, being regarded by those who hold to the Ordo- 

 vician age of the schist as a less metamorphosed phase of this formation 

 which is very similar to the Hudson River slates and phyllites north of 

 the Highlands. This phyllite has been regarded by all who have studied 

 it as of Ordovician age. 



There is an interval of a little over one and a half miles between the 

 nearest outcrops of phyllite and schist. As has already been remarked, 

 where the schist southeast of Peekskill is at a sufficient distance from the 

 contact metamorphic effects of the Cortlandt intrusive, it does not show as 

 marked metamorphism as does the typical Manhattan schist farther south 

 and southeast. Feldspar is almost entirely absent, and sericite is an 

 abundant constituent of the rock. The schists north of Croton Village 

 also are not as metamorphosed as the typical Manhattan schist of south- 

 eastern New York. Some of the garnetiferous staurolite mica schist very 

 similar to that described from north of the Highlands is also present here. 

 Clearly transition phases between phyllites and typical mica feldspar 

 schist similar to those north of the Highlands are present in the area 

 south of Peekskill and north of Croton Village, but in most cases they 

 have been obscured by the contact metamorphism accompanying the in- 

 trusion of the Cortlandt series. As seen from the description of the schist 

 north of the Highlands, the transition from phyllite to schist may take 

 place within a comparatively short distance. It is reasonable to believe, 

 therefore, that the Peekskill phyllite may represent a less metamorphosed 

 phase of the Manhattan schist. 



Of those who have made a careful study of the Manhattan schist, Dr. 

 Charles P. Berkey''^ has given the best arguments against the correlation 



M N. Y. state Mus. BuM. 107, pp. .361-378. 1907. 



