GEOLOGY AND PALEONTOLOGY OF THE SCHOHARIE VALLEY 133 



Chapter 3 



STRATIGRAPHY OF THE SCHOHARIE REGION (continued) 



The Lower Devonic rocks of the region 



The Schoharie region has long been famous for the clear 

 differentiation and normal succession of the rocks of the Helder- 

 berg series and their immediate successors up to the base of the 

 Onondaga limestone. The rocks now classed as Helderbergian 

 [see table] were formerly included in the upper part of the 

 Siluric, under the name of Lower Helderberg group. ^ The Tent a- 

 culite or Manlius limestone was included in the Lower Helder- 

 berg group, for it was generally held that sharp division lines are 

 necessary to separate formations. It is only within the last few 

 years that the Devonic age of the higher portions of the Lower 

 Helderberg group has been established, chiefly by the paleontologic 

 labors of Clarke and Schuchert, and that the dividing line between 

 Upper Siluric and Lower Devonic was definitely established at 

 the top of the Manlius limestone. Till recently the formations 

 under consideration have been known by the names given them 

 by the early geologists, among whom John Gebhard esq. and 

 Lieut. W. W. Mather were specially concerned with the Helder- 

 berg rocks. Paleontologic names were largely selected for the 

 formations /by these geologists, but these have since been replaced 

 by names selected from typical localities, mostly in the Hud- 

 son valley. The following table shows the Lower Devonic 

 formations with the present and former names, the highest beds 

 being placed at the top of the table and the current nomenclature 

 at the left. 



■^Tbe Upper Helderberg group included the Esopus and Schoharie grits 

 and the Onondaga limestone. 



