254 ANNALS NEW YORK ACADEMY OF SCIENCES 



Faulting has occurred in the region since the period of folding. In 

 places along the northern borders of the Highlands, the pre-Cambrian 

 gneisses have been thrust upon the paleozoic strata. This faulting prob- 

 ably accompanied the crustal movements which involved eastern North 

 America at the close of the Paleozoic. ''■ 



Comparison of Inwood-Manhattan and Poughquag-Wappinger- 



HuDsoN River Series 



As has already been shown, there is still a marked difference of opinion 

 as to the relationship of the Inwood-Manhattan series south of the High- 

 lands to the Poughquag-Wappinger-Hudson River series to the north. 

 One view is that they are equivalents, while the other is that the Inwood- 

 Manhattan series consists of much older formations belonging to the pre- 

 Cambrian. The arguments in favor of their being the same in age will 

 be taken up first, and then those against such a correlation will be con- 

 sidered. 



Probably the strongest argument in favor of the correlation of the 

 two series is the fact that they represent almost the same lithological 

 succession of formations, the only difference being that the one is more 

 metamorphosed than the other. South of the Highlands, a quartzite is 

 occasionally found overlying the gneiss, on top of which rests the Inwood 

 limestone, followed by the Manhattan schist. ISTaturally, this quartzite 

 has been correlated with the Poughquag quartzite north of the High- 

 lands ; the Inwood limestone has been regarded as the equivalent of the 

 Wappinger, and the Manhattan schist has been considered the represen- 

 tative of the Hudson River slates by many geologists. The upper two 

 formations in each case correspond quite closely in thickness, but the 

 Poughquag quartzite on the other hand is usually much thicker than the 

 Lowerre quartzite south of the Highlands, even where this is developed 

 to its greatest extent. 



From the descriptions of the Hudson River shale and slate and the 

 Manhattan schist already given, it has been shown that the latter was 

 derived from a sediment very similar in composition to that of the for- 

 mer, and where it has been sufficiently metamorphosed, as in the eastern 

 portion of Dutchess County, it has been converted into a mica feldspar 

 schist practically identical with the Manhattan schist. Likewise, the 

 Wappinger limestone of the Dover-Pawling Valley in eastern Dutchess 

 County also shows the same coarse crystalline texture that the Inwood 

 limestone possesses and has tremolite and phlogopite developed in it to 

 an equal extent. ■ '^ 



