160 NEW YORK STATE MUSEUM 



loses its carbonate of lime and becomes a gritty yellowish sand- 

 stone. It is found only from Cherry Valley eastward, extending 

 round the front of the Helderbergs and along the hills west of 

 the Hudson, but does not appear to be known in Pennsylvania. 



Upper Helderberg or Corniferous Limestone 



This which lies above the Schoharie grit, Cauda galli grit and 

 Oriskany sandstone, and where these are wanting, together with 

 the Lower Helderberg, as in western New York, rests immedia- 

 tely on the waterlime group, is one of the most widely known and 

 useful limestones of the state. The lower portion, from 10 to 20 

 feet in thickness, is generally a coarse-grained crystalline gray 

 rock, and, when free from chert, working well under the hammer 

 and chisel, and often taking a good polish as a marble. It is 

 called, from being very extensively quarried in Onondaga county, 

 the Onondaga Limestone. It is easily traced from near Rondout 

 on the Hudson to the Helderbergs in Albany county, where its 

 outcropping edge turns westward, and extends past Schoharie, 

 Cherry Valley, Bridgewater, Oriskany falls, the falls of the Chit- 

 tenango below Cazenovia, Split Rock, Auburn, Phelps, Le Roy, 

 and Williamsville to Black Rock. Through nearly all this dis- 

 tance it preserves its well marked character, and is extensively 

 used in building. 



The upper portion of the group is what was originally called 

 the Corniferous limestone, from its containing beds and nodules 

 of hornstone or chert: it is usually from 30 to 50 feet thick, a 

 bluish or grayish rock, often having some shale interstratined 

 with it. Though these two portions of the Upper Helderberg 

 limestone are in most places very distinct, yet in others, especially 

 in the west, they seem to run together or blend in one mass; so 

 that they are now regarded only as local varieties of a single rock. 



Upper Devonian Rocks 



In the Upper Helderberg group, we have the last or highest 

 formation of limestone of any considerable extent or thickness 

 in the state. All the southern counties, lying above or south of 



