272 C. Ccdlaway — L. Helderherg Group of N. York. 



ing a thin cornice overhanging the shale are a few feet of coralline 

 limestone, the meagre representative of the Niagara (Wenlock) group 

 of Western New York, We next come to the Water-lime rock, so 

 named from its use for hydraulic cement, a dolomite rendered impure 



Section 2. 



a = Hudson Eiver group. 

 b = Clinton shales. 

 c = Niagara Limestone. 

 c^ = "Water-lime group (Onondaga Salt 

 group). 



<f = Lower Helderberg group : — 



<^i =Tentaculite Limestone. 



d^ = Lower Pentamerus Limestone. 



<^^ = Deltliyris Shaly Limestone. 



<f^= Upper Pentamerus Limestone. 

 c = Upper Helderberg group. 

 /= Hamilton group. 



by silica, alumina, and iron peroxide. It represents the great saline 

 series of Onondaga county, the Onondaga Salt group, the equivalent 

 of the upper part of our Wenlock series. Next in order we have the 

 four members of the Lower Helderberg. First, a thin band of a 

 clinking limestone full of a Tentaculite, the Tentaculite Limestone. 

 Then comes the Lower Pentamerus Limestone, a massive thick-bedded 

 series, 50 feet in thickness, characterized by the abundance of Penta- 

 merus galeatus. The preceding limestone beds form a bold escarp- 

 ment, in some places falling down in a vertical precipice. Overlying 

 the Lower Pentamerus Limestone is the Catskill or Delthyris Shaly 

 Limestone, a calcareous shale with impure thin-bedded limestones. 

 Being much softer than the limestones above and below, this shale is 

 hollowed out, and forms a gentle slope rising up to the fourth sub- 

 division, the Upper Pentamerus Limestone, a thin band which ovei'- 

 bangs the shaly beds in a well-marked cornice. It is characterized 

 by the abundance of another species of Pentamerus, P. pseudogaleatvs, 

 The different members of the Upper Helderberg succeed, capped by 

 the Corniferous Limestone. A profile of the hill thus shows three 

 bold steps or terraces formed respectively by the Lower Pentamerus, 

 the Upper Pentamerus, and the Corniferous Limestones. With the 

 last of these we have not here to deal. 



2. Stratigraijliical evidence. — Some American geologists have main- 

 tained that the Lower Helderberg group is the easterly extension of 

 the Niagara series of Western New York, the equivalent of our 

 Wenlock. This identification appears to be based upon certain pala3- 

 ontological resemblances between the two formations, which I shall 

 discuss farther on. It has probably received support from the fact 

 that both the Niagara of Western New York and the Lower Helder- 

 berg of the Eastern end of the State hold a similar relation to the 

 overlying Upper Helderberg Limestone. In the Helderberg range 



