DEVONIAN. 299 



Neither of the Helderbergian zones can be regarded as the deeper-water facies of the littoral 

 Oriskany, not only because the fauna of the latter has a more decided Devonic aspect, but also 

 for the fact that wherever the two formations are present the Oriskany always overlies the 

 Helderbergian. As far as known, there is no interlamination, and in New York, where the 

 stratification is simple, there is a regular sequence. Where the older Oriskany is absent there 

 is a slight unconformity between the Helderberg and the later Oriskany. This unconformity 

 becomes a decided one in going from eastern to central New York, because the later Oriskany 

 gradually comes to overlie successively the various members of the Helderbergian and finally 

 the Cayugan. 



The Oriskany sandstone is thus described by Hall : ^^^ 



The Oriskany sandstone everyvrhere succeeds to the upper meipibers of the Lower Helder- 

 berg group and at several points extends beyond the known geographical limits of the latter. 

 In the greater number of localities within the State of New York the transition from the upper 

 calcareous beds of one group to the siliceous or sandy beds of the other is very abrupt, while 

 in other instances there is an intermingling of calcareous matter in the lower beds of the sand- 

 stone. In t^iese instances, however, as well as in others, the sUiceous material appears to have 

 been to a considerable degree in the condition of gelatinous sUex, producing a rock approaching 

 in character to homstone ; while other examples present an appearance as if the grains of silex 

 had been softened, or agglutinated by a siliceous paste. In its more fossiliferous parts the rock 

 is a mixture of silica and carbonate of lime, and the action of the weather, dissolving and remov- 

 ing the latter, leaves a grayish-brown porous mass, embracing the casts of the interior and 

 molds of the exterior of the fossil shells. In many places the rock consists of a sandstone of 

 nearly pure white, or graduating from white to buff-colored; in more southern localities it often 

 presents the aspect of a siliceous limestone, not differing greatly from the succeeding limestones. 



Schuchert ^"^ gives the following account of the character of the Oriskany in 

 New York : 



In a general way it may be said that the Oriskany formation extends with many interrup- 

 tions along the eastern and northern flanks of the Helderberg Mountains of New York. Along 

 the northern side the Upper Oriskany only is known to be present, exceedingly variable in 

 thickness but never more than 30 feet, diminishing in volume and resting westwardly upon the 

 successive lower horizons of the Helderbergian and finally on the Siluric. In the region of 

 Cayuga Lake it is sparingly present, and is practically absent west of Ontario County, the 

 Corniferous or Onond,aga then resting directly on the Salina or Waterlime. Bej^ond the Niagara 

 River, to the northwest of Cayuga, in Ontario, the Oriskany reappears irregularly over a very 

 limited area, again overlying the Salina, and is from 6 to 25 feet thick. Southerly, along the 

 western side of the Hudson River, the Upper Oriskany is very intermittent and often but 2 or 

 3 feet thick. On Becraft Mountain there is an outlier of Oriskany. In Orange County the 

 Oriskany again appears to thicken, and in the Neversink Valley the thickness is about 125 feet, 

 and at tliis point it is intimately connected with the Helderbergian. In New Jersey, and 

 particularly in the eastern Appalachian folds of Pennsjdvania, the Oriskany in its lithologic 

 character is ever changing from sandy shales, sandstones, and chert beds to coarse conglomerates. 

 Its thickness also increases from north to south ; in northeastern Pennsylvania it is from 50 to 

 125 feet thick, and on the Lehigh River, below Bowmans, it is fully 200 feet. 



Clarke ^^^'^ has thus stated the distribution and relations of the Helderbergian 

 and Oriskany: 



In New York the deposits constituting the earliest members of the Devonic series are, at 

 the bottom, (1) the Helderbergian and, overlying, (2) the Oriskanian. There is a demonstrated 

 _gradation of the sediments and the faunas of the lower into the higher, and those at the summit 

 of the Helderberg series — Port Ewen beds — carry so large a representation of Oriskany species. 



