NIAGARA AND LOWER HELDERBERG GROUPS. 127 



of geology of one of these names, heretofore adopted, and in 

 general use wherever geology is written or spoken. 



I will here cite a single sentence from the paper referred to : 



"We recollect that, on visiting the locality of these so-called 

 Lower Helderberg limestones in the Schoharie valley some 

 years ago, we observed these limestones resting immediately 

 upon undisputed Lower Silurian beds there ; and, in explana- 

 tion of their occurrence in this apparent abnormal position, we 

 were told that the Niagara group was supposed to have thinned 

 out to the eastward, and that these Lower Helderberg lime- 

 stones took their place." 



Fortunately or unfortunately there is no evidence given as 

 to the authority or by whom " we were told^ that the Niagara 

 group was supposed to have thinned out to the eastward. In 

 the first place let us inquire as to the fact of the Lower Helder- 

 berg " limestones resting immediately upon undisputed Lower 

 Silurian beds there " or elsewhere. Having been familiar with 

 the Schoharie valley, and having made numerous sections, and 

 explored long lines of outcrop in that valley, in the Cobleskill 

 valley and in the Helderberg, I have never been able to see the 

 Lower Helderberg limestones resting upon Lower Silurian 

 rocks. On the contrary, the section of strata everywhere 

 shown is the following, as given on the diagram, from the 

 sandstones of the Hudson river group to the Oriskany sand- 

 stone : 



Oriskany sandstone. 

 f Upper Pentamerus limestone. 

 Lower Helderberg J Shaly limestone. 



group. | Lower Pentamerus limestone. 



[Tentaculite limestone. 



Water-lime formation. 



"Niagara group = Coralline limestone. 



Green shales with Iron pyrites. 



Lower Silurian ■! Sandstones and shales of the Hudson 

 1 river group. 



Everywhere the lower member of the Lower Helderberg 

 group is unmistakably separated from the sandstones of the 



