236 J. Barrell — Tipper Devonian Delta of the 



within it, nor is any change along the axis of the syncline to 

 be noted which suggests that the sands and gravels were depos- 

 ited in a narrow inlet, subject to lateral transportation of sedi- 

 ments and weak wave action. 



The Green Pond conglomerate is overlain by the Longwood 

 shales 200 feet in thickness and of red color, succeeded by the 

 Decker limestone 50 feet thick, and carrying Cayugan fossils. 

 Above the Decker limestone occurs the Kanouse sandstone 

 (Newfoundland grit of the New Jersey report) 215 feet in 

 thickness and carrying a mixed Oriskany-Corniferous fauna. 

 The sequence is thus similar to that of the main Appalachian 

 geosyncline but the beds above the Silurian conglomerate are 

 thinner and certain horizons are probably missing. There is, 

 however, no suggestion of local sediments from the walls of an 

 estuary. On the contrary, the evidence suggests that the 

 region \&y nearer to the land of Appalachia and the bottom 

 was less subject to subsidence. Hence thinner deposits of 

 sediment were apt to be laid down and the material on the 

 whole was coarser and less calcareous. Over such a zone the 

 minor crustal oscillations are more apt to bring about tempo- 

 rary erosion followed by overlap. Certain beds above the 

 Longwood shales appear to be absent in places.* In this 

 region, Darton notes the difficulty of discriminating between 

 overlap and overthrust, but states that on the northwest the 

 Helderberg limestone rests directly on Cambrian limestone 

 with no possibility of an intervening fault. f This suggests a 

 pre-Helderberg warping of some extent, perhaps while the 

 Green Pond conglomerate was still an unconsolidated gravel. 

 In this region the Hamilton is represented by the Pequanac 

 shale (Monroe shales of Darton), consisting perhaps of a thou- 

 sand feet of dark, thick-bedded shale, somewhat sandy toward 

 the top and containing a Hamilton fauna. According to 

 Darton it also overlaps all of the preceding formations,:}; but 

 the character of the sediment, like that of the preceding for- 

 mations, does not indicate a local source. This is the last over- 

 lap known, as the Pequanac shale grades up into the Bellvale 

 flags, a formation between 1600 and 2000 feet in thickness. 

 The lower part of the Bellvale flags contain a Hamilton fauna. 

 Plant beds of middle Devonian age are found in this forma- 

 tion, marine fossils fail in the upper portion, and it seems pos- 

 sible that here the continental phase of sedimentation began 

 before the close of Hamilton time. So far as known there is 

 no diminution in the thickness of the beds of the Hamilton 

 group in passing eastward from the Delaware Biver, where 



* Kummel and Weller, loc. cit., p. 20. 



f Geologic relations from Green Pond, New Jersey, to Skunnemunk Moun- 

 tain, New York, Geol. Soc. Am., Bull., v, 391, 1894. 

 JLoc. cit., p. 392. 



