NIAGARA AND LOWER HELDERBERG GROUPS. 125 



In the Helderberg mountains in Albany county, and in 

 Schoharie, along the valley of the Schoharie creek, and in the 

 Cobleskill valley, we find everywhere a series or group of lime- 

 stones, of which we distinctly recognize four members ; these 

 are known in the ascending order, as Tentaculite limestone, 

 Lower Pentamerus limestone, Shaly limestone and Upper 

 Pentamerus or Scutella limestone. There is, in some 

 places, for miles in extent, a mass of Stromatopora limestone 

 between the Tentaculite and Lower Pentamerus limestones* 

 These together constitute the Lower Helderberg group, 

 forming in Albany county the base of the Helderberg moun- 

 tains, and everywhere succeeded by the Oriskany sandstone, 

 Cauda-galli and Schoharie grit and Corniferous limestone ; 

 and these, in the summits of the hills, by the arenaceous shales 

 of the Hamilton group. 



This group of limestones is everywhere characterized by the 

 presence of fossils, often in immense numbers, and specifically, 

 with very few exceptions, quite unlike the fossils of the rocks 

 above or below this horizon. From the Helderbergs, and the 

 valley of the Schoharie, we are able to trace the formation to 

 the westward through the northern part of Otsego, and the 

 southern part of Herkimer and Oneida counties ; and, accord- 

 ing to Mr. Yanuxem, it is recognized in the eastern part of 

 Onondaga county, by the presence of some of its peculiar fos- 

 sils. From the Helderberg mountains the group gradually 

 thins to the westward ; and in Herkimer county the divisions 

 of the several members are scarcely recognized, the entire mass 

 becoming more completely calcareous, but still charged with 

 an abundance of the characteristic fossils of the group. West 

 of Onondaga county the place of the formation is often recog- 

 nized by a stratum of hard, compact limestone lying beneath 

 the Oriskany sandstone.* It is quite evident that the force of 

 the entire group diminishes in a westerly direction. 



Returning to the point of departure in the Helderbergs, w& 

 are able to trace the rocks of this group, in their clearly 

 defined and unmistakable characters, through the eastern coun- 

 ties of New York to the limits of the State of New Jersey. In 



* In some former Reports on the geology of the western counties, this rock is 

 described as worn or eroded previous to the deposition of the Oriskany sand 

 stone. 



