SILURIAN. 241 



Immediately above the Green Pond conglomerate, and conformable with it, is a soft red 

 shale [Longwood shale], in which an irregular cleavage is usually so highly developed that the 

 bedding planes can be determined only with difficulty. The formation is not known to contain 

 fossils, but, as it rests directly upon the Green Pond conglomerate and is followed by a hme- 

 stone carrying a Salina fauna, it is probably of Salina age. Its stratigraphic position is, in 

 general, the same as that of the High FaUs formation, but the two may not be exactly 

 .synchronous. 



The higher Silurian and the Devonian formations of New Jersey occur either in WaUpack 

 Ridge, which lies along the northwestern border of the State in the upper Delaware Valley, or 

 in the narrow belt of Paleozoic rocks in the midst of the highlands in the Green Pond Mountaia 

 region. In Wallpack Ridge they aggregate 1,300 feet of more, while in the Green Pond 

 Mountain region they have a thickness of about 4,000 feet, of which aU but 250 feet are 

 referable to beds higher than any of those along Wallpack Ridge. 



The top of the High FaUs shale in New Jersey is everywhere buried by glacial drift which 

 also conceals the beds immediately superjacent. The next recognizable formation is the 

 Poxino Island shale, a buff or'greenish calcareous shale in thin layers and nonfossiliferous so far 

 as known. Its outcrops along the base of Wallpack Ridge in the upper Delaware Valley are 

 few, small, and widely separated, and very little is known regarding it. In the adjoining 

 portion of Pennsylvania it is reported to be 200 feet in thickness and to rest on a thin limestone 

 formation which in turn rests on the High FaUs shale. It is not known to occur in the Green 

 Pond Mountain region. 



A fine-grained, compact bluish-gray banded limestone, known as the Bossardville lime- 

 stone, lies conformably upon the Poxino Island shale in WaUpack Ridge. It increases in , 

 thickness from 12 feet at the New Tork State line to about 100 feet where it crosses the Dela- 

 ware River into Pennsylvania. Owing to its marked banding it was for many years laiown as 

 the "Ribbon" limestone and was correlated by Cook and later geologists with the Ribbon or 

 Manlius limestone at Rondout, N. Y. In reality it lies below the Manhus limestone. It is only 

 sparingly fossUiferous but is immediately succeeded by a series of beds containing a weU-defined 

 Salina fauna. It has not been recognized in the Green Pond Mountain belt, but this may be 

 from lack of exposures. 



Under the name Decker Ferry formation a series of beds has been described, which are 

 chiefly limestones at the north and calcareous sandstones at the southwest. Their thickness is 

 52 feet at the Nearpass quarry near Tristates, where the section can be accurately measured. 

 Thin bands of more or less fissUe green shale separate the limestone beds. A thin band of red, 

 crystalline, highly fossUiferous limestone occurs about the middle of the series and is a striking 

 feature. The lower 42 feet of these beds as exposed at the type locality are correlated " with 

 the Wilbur limestone (the so-called "Niagara" or "CoraUine" limestone of HaU and other 

 authors) and the "black cement" beds — that is, the Salina "water lime" of the Rondout section 

 of New York. These form the top of the Salina group, the base of which in New Jersey is the 

 base of the Shawangunk conglomerate. The upper 10 feet of the Decker Ferry series contain 

 fossUs, particularly in the lower half, which render necessary their correlation with the CobleskiU 

 limestone of eastern New York. 



In the Green Pond Mountain region isolated outcrops of impure limestone occur a short 

 distance above the Longwood shale, which contain a fauna that correlates them with the lower 

 beds of the Decker Ferry formation — that is, to the part referable to the Salina group. 



Along the upper Delaware the beds immediately above the Decker Ferry limestone and 

 referred to the Rondout consist of more or less earthy shales and limestones the thickness of 

 which is 39 feet. They are usually only sparingly fossUiferous, although in some beds the 

 crustacean Leperditia is abundant. A typicaUy marine fauna, with an abundance of bracM- 

 opods, trUobites, etc., is conspicuously absent in these beds. In general lithologic features 

 this formation resembles the Rondout as developed in New York State, but the cement beds 

 which are so characteristic of this formation farther north are not present here. 



a Hartnagel, C. A., Bull. New York State Mua. No. 69, 1903, p. 1152. 

 48011°— 12 16 



