374 STEVENSON 



THE ORISKANY SANDSTONE 



The Oriskany is thin at Schoharie, not more than ten feet. 

 The contact with Upper Pentamerus was not seen but on the 

 schoolhouse hill and on West mountain the concealed space is 

 not more than i8 inches. The rock is rarely found in place as 

 it decays readily and the crop becomes covered. One exposure 

 on the schoolhouse hill shows J feet. On West mountain the 

 interval from the highest observed layer of the Pentamerus 

 to the top of the Oriskany is barely i 2 feet. The rock is bluish 

 gray, slightly calcareous sandstone with much ferruginous mat- 

 ter as cementing material. Unweathered, it is very hard, but 

 weathered it is rusty yellow and very tender. 



The change from Helderberg to Oriskany is abrupt at Scho- 

 harie and according to Mr. Darton's observations it seems to be 

 equally so throughout the region. Professor Hall once stated 

 in conversation that the break at this horizon is one of the best 

 defined in the State of New York. But the case is different 

 farther south in the Appalachian region. The transition is very 

 gradual in southern Pennsylvania, there being as the transition 

 bed a silicious limestone, 20 feet thick, very cherty, whose 

 whitened fragments occur abundantly on every Oriskany ridge 

 in Bedford county. This bed contains the Helderberg Favosites 

 along with such typical Oriskany forms as Spirifcr ai'cnosns 

 and PUilyostoma veiitricosiiin. The section is almost complete 

 at Hyndman, where the quarries are extensive. This tran- 

 sition bed is persistent southward, being present as the attenuated 

 representative of the Oriskany and Helderberg at several lo- 

 calities in the Valley of Virginia, where those formations thinned 

 out against the old shore-line. The intimate relation between 

 these formations seen in southern Pennsylvania is equally clear 

 in southwestern Virginia, where, however, the Helderberg be- 

 comes silicious in the upper portion and the Oriskany contains 

 so many Helderberg forms that the writer during his first exam- 

 ination of the region thought it the Helderberg. In New 

 York the Oriskany does not contain crinoids, but such forms 

 are by no means rare in Maryland and southward. 



