BUFFALO SOCIETY OF NATURAL SCIENCES 13 



The contact of the Cobleskill limestone with the underlying 

 Bertie limestone is not well marked. Between the two there is a 

 gradual transition through two feet or more. 



The contact of the Cobleskill with the overlying Onondaga 

 limestone is very definite and well marked. Wherever the upper 

 layers of the Cobleskill are exposed, as in quarries, the upper 

 surface is found to be wavy or hummocky, an effect caused by 

 irregular depressions of a depth of a foot or more. These 

 depressions, and some channels observed in the Bennett quarry, 

 seem to mark a period of erosion. The depressions are coated 

 with a thin deposit of green shale, which follows the contours of 

 the hollows and ridges to the depth of an inch or less. Above 

 this shale the lowest layers of the Onondaga limestone follow 

 the contours of the depressions in the Cobleskill, being separated 

 from it by the thin shale. 



The Cobleskill was formerly of much economic importance 

 owing to its burning to a cement. Portland cement has now 

 supplanted it. It is also used in a limited way as a building 

 stone. 



This formation attains a thickness of 9 feet at Falkirk and 

 14 feet at Akron which is the greatest thickness in Erie county. 

 In the Buffalo quarries it ranges from 2 to 5 feet. 



Oriskany Horizon. 



In southeastern and eastern New York are heavy deposits 

 of sandstones, conglomerates and limestones which have received 

 the name of Oriskany sandstone from their exposure at Oriskany, 

 Oneida county. These arenaceous deposits are underlain in 

 eastern New York by the heavy beds of the Helderbergian group 

 which constitute the lowest members of the Devonic system. 



In Erie county the Oriskany sandstone is absent. The upper 

 surface of the Cobleskill presents an eroded appearance. Its 

 regular horizontal bedding is broken by irregular hollows and 

 depressions similar in all features to the erosion features of a 

 limestone surface exposed to the action of streams or waves. In 

 the bottoms of the depressions are thin layers of green shale and 

 a conglomerate of water-worn fragments of limestone cemented 

 together with quartz. This green shale and the accompanying 

 breccia seem to represent the detritus of a somewhat prolonged 

 erosion of a large superficial area of the Cobleskill limestone and 

 this erosion is supposed to correlate with the beach deposits of 

 Oriskany time. 



