654 NEW YORK STATE MUSEUM 



short duration, lasting only, as we shall endeavor to show, till 

 early Hamilton (Marcellus) time, when the subsidence, which in 

 the meantime affected the greater part of the southeastern 

 fourth of the continent, reopened the Oriskanian channel and, 

 extending it eastward, allowed invasion from that direction. 

 This Marcellus invasion produced considerable intermingling of 

 the Atlantic and Mississippian faunas, specially in those laid 

 down in the modified but resubmerged Cumberland basin. 



In the Skunnemunk and Green Pond mountain region, the 

 former in southeastern New York, the latter in, New Jersey, 

 there is a series of coarse deposits apparently occupying a syn- 

 cline. The oldest formation above the presiluric deposits is 

 the Green Pond conglomerate, supposed to be of the age of the 

 Shawangunk farther north. From this on, deposition appears 

 to have been continuous to the close of the Helderbergian, when 

 this area, in common with the Cumberland basin to the west of 

 it, was affected by the elevation of the eastern side of the con- 

 tinent. Resubmergence began here with the Monroe shales, 1 

 which rest on Oriskanian strata, and continued through the 

 skunnemunk Bellvale flags into the Skunnemunk conglomerate, which Darton 



trough and ° ° ' 



in r i? atlons suggests " may represent the Oneonta " or " the formation may 

 be the equivalent of the coarse beds of the Chemung." Fossils 

 from the Monroe shales sent by Darton to Hall were pronounced 

 by the latter to be of " typical lower Hamilton (group) species." 2 

 The Bellvale flags contain Tropidoleptus carinatus, 

 Spirifer mucronatus, and, more commonly, land 

 plants, recalling those described by Dawson from the Gaspe* 

 sandstones. According to Ries the total thickness of the De- 

 vonic deposits (succeeding the Esopus or Oriskany) in the 

 Skunnemunk and Bellvale mountains of New York, is about 1500 

 feet; while Darton gives a thickness of 5400 feet for the equiva- 

 lent series in the Green Pond area of New Jersey. This differ- 

 ence in volume is cited in support of our opinion that the great- 



t . — . — — ■ ■ 



1 Darton. Geol. soc. Am. 1894. v. 5; Ries. N. Y. state geol. 15th an. 

 rep't 1897. 1898. 1:403-4, 410-24. 



2 Darton, op. cit, p. 375. 



