380 New York State Museum 



Oriskany sandstone occurs as a series of thin lentils, 

 sometimes not appearing at all or represented only by 

 scattered sand grains or sand fillings in crevices in the 

 rock below. This is considered the clastic initial deposit ot 

 the Onondaga (Ulrich). In the east the Oriskany forma- 

 tion is represented by both arenaceous and calcareous sedi- 

 ments. In the Cobleskill-Schoharie area the rock is a 

 mixture of quartz and lime grains. When the rock is 

 exposed the lime is commonly dissolved out leaving a 

 brown, porous sand-rock in which the fossils are beau- 

 tifully preserved as both internal and external molds. 

 The formation in this area has a maximum thickness of 

 five or six feet, in some places being only one or two 

 feet or less thick, perhaps missing in others'. In the 

 northern Helderberg area the rock is similar, with a 

 maximum thickness of about four feet. Because of the 

 flinty nature of the rock it is very resistant and wherever 

 the beds are more or less horizontal forms a level plat- 

 form or terrace, the softer Esopus beds above having 

 been eroded, with the surface covered with the char- 

 acteristic worm burrows Taonurus cauda-galli or "Cock- 

 tails" which also mark the Esopus shales. Going south- 

 ward from here the rock soon changes in character and 

 becomes a chert or cherty limestone. In the Catskill area 

 in Greene county it no longer has its typical appearance, 

 though characterized, as the typical beds, by the brachio- 

 pod Spirifer arenosus, and still is only a few feet in 

 thickness. Farther southward it thickens more and more 

 and highly fossiliferous limestone beds come in at the 

 top and still farther south a basal pebble conglomerate 

 (18 to 20 feet thick) also of Oriskany age. To that fos- 

 siliferous limestone in Ulster county Chadwick ('08) has 

 given the name Glenerie limestone from its occurrence 



