GUELPH FAUNA IN THE STATE OF NEW YORK 133 



oblongus is much more abundant here than at the north." The 

 appended list of fossils includes, besides Niagaran corals and crinoids: 

 Trimerella ohioensis, T. grandis, Obolus conradi, Pen- 

 tamerus oblongus, Murchisonia macrospira, M. laphami, 

 Platystoma niagarense, Megalomus canadensis, Trocho- 

 ceras desplainense, Orthoceras abnorme, Calymmene 

 niagarensis. 



From Dr Orton's original description of this section ' we select the 

 following data : The Guelph or Cedarville limestone is a massive magnesian 

 limestone (carbonate of lime 54.25$, carbonate of magnesia 43.23$) varying 

 in thickness from 20 to 90 feet. Even where the whole of the original 

 deposit is present, as in sections where it is found inclosed between higher 

 and lower formations, it has the wide limits already given. It contains 

 bituminous matter distributed through its substance, and it is pointed out 

 that the oil-bearing limestones of Chicago belong to the same horizon. 

 This formation is often destitute of distinct bed lines in its structure. It is 

 acted on quite easily by atmospheric agencies and by its unequal weath- 

 ering the faces of the cliffs that it forms are rough and irregular. 



It will be noticed that this rock shows notable agreement with the 

 Guelph rocks of New York. 



Pentamerus oblongus is the most common fossil of the Guelph 

 through this region and further west and it gave the name to the formation. 

 In New York and Canada this shell is a Clinton and Niagaran species but 

 in Ohio it appears in full force only in the upper Niagaran limestone and 

 Guelph. Certain layers are heavily charged with Megalomus while Trim- 

 erella is also very abundant. Large gastropods and corals show in many 

 places. The Guelph is overlain by and interstratified with the Hillsboro 

 sandstone and is the only known instance of distinct shore conditions 

 recognizable during the Guelph stage. 



Orton also described the section at Yellow Springs, Greene co. where 



'Rep't of Progress, 1871, p. 278 ft seq. 



