Related Formations. 



15 



New York geologists above the Utica slate horizon, and the same 

 strata in Pennsylvania and Canada and their western extension de- 

 signated as the Nashville and Cincinnati groups. 



SUPLEMENTAEY NOTE. 



This paper was prepared in January of this year, 1879, and as the 

 third volume of the Geology of Ohio was not received until late in 

 February, the following references are added as bearing on the nomen- 

 clature adopted by the writer in speaking of the Hudson River group. 



Prof. J. S. Newberry has a reference in the third volume of 

 the Geology of Ohio, which mentions the statements made in the 

 first volume of the same work, relating to the propriety of retaining 

 the term Cincinnati group, for the strata exposed in southern Ohio 

 which have received that name. 



On page 3 of the third volume the following passage occurs : 



" In the state of New York, the differences between the Trenton 

 and the Hudson groups, are chiefly local and lithological nearly all 

 the fossils of the Hudson being found in the Trenton. The only 

 fossils characteristic of the Utica slate, are graptolites which seem to 

 have grown in great profusion in certain shallow and quiet parts of 

 the lower Silurian sea." 



The difference between the Trenton and Hudson groups, as estab- 

 lished in New York are not local or entirely lithological. From 

 Lake Huron, across the province of Ontario to New York State and 

 thence by the way of the Black river, Mohawk, Hudson, Lake Champ- 

 lain and St. Lawrence valleys to Anticosti and south-west from the 

 valley of the Hudson to Virginia, the differences are essentially the 

 same. The black, bituminous shale forms a distinct horizon between 

 the Trenton and Hudson groups. 



Viewed in its palseontological aspect we find one hundred species 

 of fossils, fifty-four of which are limited to the formation (Utica), of 

 these thirty-three are graptolites in nine genera. There are also of 



Algje, 3 genera, 4 species. 



Bryozoa, 1 genus, 1 " 



Brachiopoda, 2 genera, 3 " 



Lamellibranchiata, 3 " 3 " 



Gasteropoda, 1 genus, 1 " 



Cephalopoda, 1 " 1 



Pteropoda, 1 " 1 " 



Crustacea, 2 genera, V " 



* Proc. Amer. Assoc. Advt. 8ci., 1877. 



