OEISKANY FAUNA OF BECRAFT MOUNTAIN 13 



been largely leached out for a considerable depth on all exposed sur- 

 faces, only a porous residuum remaining. This light, rusty and firm 

 rotten stone retains the external and internal casts of the fossil remains 

 with which it is filled, in exquisite detail and forms excellent material 

 for study. Only by hastening nature's process with acid can the fossils 

 be made out from the black and cherty or unchanged calcareous cores 

 of this rock. 



It is not easy to estimate the actual thickness of these strata at 

 this place, as it would appear that they have been partly eroded, but 

 there is no evidence above them of the black chert beds which ter- 

 minate the Oriskany deposits in the Ulster, Albany and Schoharie 

 county sections, nor of the characteristic white quartz sandstone of the 

 central sections. These beds rest on an argillaceous limestone, which 

 seems to be present in only slight force and is almost wholly if not 

 quite concealed ; the " upper shaly " or Kingston limestone, blocks of 

 which are frequently found in close association with the Oriskany and 

 so closely resemble the latter that considerable care and experience are 

 requisite to avoid confounding the two. The author has therefore taken 

 utmost care in making up the list of species of the Oriskany to 

 eliminate all this "upper shaly" material from consideration. This is 

 readily done after experience in recognizing the lithologic differences, 

 aided by the fact that the Kingston limestone contains but very slight 

 intermixture of Oriskany species. The Helderbergian species here regis- 

 tered, therefore, occur in Oriskany limestone and in immediate association 

 with Oriskany fossils. 



From the axis of the syncline, specially along the north and south 

 road crossing the mountain, is a ridge of gray, sandy grit with slaty 

 cleavage so strongly developed that the original bedding is entirely lost. 

 This rock covers a large area from the center of the region and constitutes 

 the high ridges which cap both of the synclinals. Prof. Davis regarded 

 all of this rock, which in places rises in very sharp escarpments, par- 

 ticularly on the east of the southern part of the road mentioned, as the 

 Cauda-galli grit (Esopus slate). I have found however in various places, 

 specially near the junction of the middle road with a crossroad from 

 the west starting in at the glue factory, that this rock contains 



