342 NEW YORK STATE MUSEUM 



NOTES ON THE SILURIC OR ONTARIO SECTION OF 

 EASTERN NEW YORK 



BY C. A. HARTNAGEL 



The Ontario section of central and western New York, as 

 developed west of the Helderberg- is subdivided into lO' 

 divisions,^ and it is from this section of the State that all but 

 one of the locality names applied to these divisions are derived. 

 Each of these divisions is more or less distinctly characterized 

 by differential lithologic features and all are fossiliferoiis.^ fl 



On the east side of the Helderberg and including the section 

 extending from Ulster county southwest to New Jersey, the 

 Ontario lacks several members of the group, while the fossils 

 found are of an age not earlier than late Salina, the lower mem-^ 

 bers of the Ontario where present being entirely without fossils. 

 The fact that the Manlius and Rondout formations alone of the 

 entire Silurio series have stratigraphio continuity across the Hel- 

 derberg, has left the outcrops of the Silurio rocks in New York 

 divided into two nearly distinct geographic areas.^ 



While the main purpose of this paper is to bring out the rela- 

 tions of the Cobleskill formation as developed in eastern and 

 southern New York, it will also attempt to show certain relations 

 of the lower members of the Ontario formation in so far as they 

 have come under the observation of the writer. The lower members 

 of the Ontario section in this portion of the State are entirely unfos- 

 siliferous and confusing in their lithologic features, and it will still 

 require considerable study to accurately locate their correct position 

 in the geologic series. This condition is brought about by the dis- 

 covery that the Cobleskill horizon is above the Salina deposits, a 

 fact which suggests that the Shawangunk grit and red shales above 

 it may possibly represent a later age than that to which they have 

 been usually referred. 



1 Clarke. N. Y, S. Mus. Handbook 19, July 1903. Table i, p. 9. 



2 While the Salina beds are sometimes regarded as being nonfossiliferous, it 

 will be observed that the Salina as now defined includes at its base the Pitts- 

 ford shale and at its top the Bertie waterhme. Both of these formations are 

 characterized by an Eurypterus fauna. 



3A third area is developed in Rensselaer county. The Ontaric is here repre- 

 sented by a single member known as the Rensselaer grit. This is generally 

 considered the equivalent of the Oneida or of the Shawangunk grit. 



