128 TWENTY-SEVENTH REPORT ON THE STATE MUSEUM. 



Lower Silurian age by three distinct and usually well-marked 

 members of the series. 



Tracing the Lower Helderberg formation from this point for 

 sixty miles westward, we have the following section : 



Oriskany sandstone. 

 Lower Helderberg j * Shaly and lower Pentamerus limestones, 

 group. I Tentaculite limestone. 



Water-lime formation. 



Onondaga salt group = Red and gray marls. 



Niagara group = Coralline limestone. 



( Green shales and sandstones with cal- 

 Clinton group = -< careous bands containing interstrat- 

 ( ified beds of red hematite. 



Medina sandstone. 



Lower Silurian = Gray and bluish-gray sandstones and 

 shales of the Hudson river group. 



Everywhere the lower member of the Lower Helderberg 

 group rests upon the water-lime formation ; and the latter is 

 always present, separating the former from the Coralline or 

 Niagara limestone. At a distance less than one hundred miles 

 farther west, in a line from Seneca or Ontario to Oswego 

 county, we have a section showing the following formations : 



Oriskany sandstone. 



Lower Helderberg group j Compact grayish-blue limestones in 



represented by (a band of a few feet in thickness. 



Water-lime formation. 



Onondaga salt group with salt 



# springs and gypsum beds, more 



than 1,000 feet in thickness. 

 Niagara group. 

 Clinton group. 

 Medina sandstone. 

 Hudson river group. 



* The Upper Pentamerus limestone is not developed as a distinct member of 

 the group. 



