108 The Position of the Cincinnati Group. 



It was separated in New York by Vanuxem into five subdivisions in 

 ascending order, as follows ; 1st, Water lime group or Tentaculite lime- 

 stone, 200 feet thick, some layers of which yield hydraulic cement, 

 from which the subdivision took its name. This group crosses into 

 Canada, where it is found 45 feet thick ; 2d, Pentamerus limestone, 30 

 feet thick, at Cherry Valley, and which took its name from the abund- 

 ance of Pentamerus galeatus found within it ; 3d, Delthyris shaly 

 limestone, 70 feet thick, in Albany county, which took its name from 

 the abundance of Sjnrifera macropleura, and S. pachoptera, formerly 

 called Delthyris ; 4th, Encrinal limestone, 25 feet thick, which took its 

 name from the quantity of broken encrinites it contains. It has also 

 been called the scutella limestone, from a shield-like pelvis of a crinoid 

 found in it ; 5th, Upper Pentamerus limestone, 75 feet thick, and 

 which took its name from the Pentamerus pseudogaleatus, with which it 

 is characterized. 



While this group is only from 100 to 200 feet thick in Ohio and the 

 western States, and only from 400 to 500 feet thick in New York, it is 

 1,720 feet thick in Pennsylvania, and at Gaspe, Canada, where it lies 

 immediately beneath the Oriskany sandstone — it is 2,000 feet in thick- 

 ness. (Geo. of Can., 1866, p. 260.) 



From these estimates we find that the' rocks belonging to the so- 

 called Silurian system, overlying the Cincinnati Group, are 7,970 feet in 

 thickness, or about one mile and a half. They contain the fossil re- 

 mains of no vertebrate animal so far as yet known. They show, how- 

 ever, the uninterrupted course of oceanic life from one group to anoth- 

 er, as the same is shown by their equivalents in Europe and other parts 

 of the world. 



Prof. Hall says : 



" The fossils of the Lower Helderberg are analagous to the fossils 

 of the Niagara Group, which is everywhere evident from comparison, 

 and the graduation is so slow, from one formation to the other, that they 

 are grouped together in one system, the Upper Silurian." 



Next above the Upper Silurian rocks come the Devonian, from Dev- 

 onshire, England. They are subdivided in ascending order, into : 1st, 

 Oriskany sandstone ; 2d, Upper Helderberg ; 3d, Hamilton Group ; 

 4th, Portage Group ; 5th, Chemung Group ; and 6th,'the Catskill Group. 



The Oriskany sandstone takes its name from Oriskany, New York. 

 It is found only 10 feet thick in Ohio, but in Illinois, Pennsylvania, 

 Maryland, New York, and Canada, its thickness varies from 100 to 

 300 feet. 



Prof. Hall says : 



" The lines of demarkation between subordinate groups, and the line 



