220 TWENTIETH REPORT ON THE STATE CABINET. 



The shales of Point Levis, with their associated Hmestones and sand- 

 stones, since termed the Quebec group, are now regarded as embracing the 

 period from the Calciferous sandstone to the Chazy limestone, inclusive. 

 This epoch therefore is entirely anterior to that of the Hudson-river 

 formation, and a careful comparison of all the species of graptolites has 

 shown that no identical species occur in the two series of rocks. 



In the present state of our knowledge, we recognize the Graptolitidae 

 as beginning their existence at the period of the Potsdam sandstone. 

 The greatest development of the family, both in genera and species, is 

 found to be at the epoch of the Quebec group. Several genera and a few 

 species are known in the Trenton formation ; and a greater development, 

 embracing most of the genera and many species, occur at the period of 

 the Hudson-river formation in Canada and the United States. In the 

 Clinton strata we have a single species of Graptolithus and a Retiolites ; 

 while Dictyonema and Inocmilis occur in the Niagara beds. In all the 

 subsequent geological formations we have found no true graptolites, and 

 the only representatives of the family consist of fragments of Diciyonema^ 

 belonging to a few species. These occur in the Upper Helderberg and 

 Hamilton formations, above which we do not yet know a species of any 

 genus referable to this family of fossils. The Grenus Graptolithus, therefore, 

 has its upper limit in the shales of the Clinton formation, and all others of the 

 family, except Dictyonema, are restricted to the Silurian system. 



The geographical distribution of the Grraptolitidse is not in all respects 

 coincident with the extent of the geological formation. Dendrograptus 

 occurs in the Potsdam sandstone of the St. Croix valley ; but neither this 

 nor any other graptolite is known in other localities of the sandstone, so far 

 as I am aware. The species of the Quebec group, numbering more than 

 all the other formations together, have been identified for a longitudinal 

 extent of about 900 miles ; Point Levis, Orleans Island, St. Anne's River 

 (Gasp6), and the western part of Newfoundland, being the principal local- 

 ities. But although the Quebec group is known to extend into Vermont 

 and along the eastern counties of New- York, I am not aware that grapto- 

 lites have been found in any authentic localities of that formation, unless 

 the Diplograptiis secalinvs of the Hoosic slates be referred to that group.* 

 With these exceptions, therefore, these fossils of the group are known 

 only in Canada and Newfoundland. 



The Trenton limestone, while furnishing two species of Graptolithus in 

 New- York, gives at the west no specimens of the genus proper ; but we 

 have one Dictyonema, a Buthograptus, and an Oldhamia ? in the same 

 formation in Wisconsin, though not elsewhere known to me at this time. 



The Utica slate at Utica abounds in the remains of graptolites, and 

 these fossils are of frequent occurrence at Oxtungo Creek, in the valley of 

 the Mohawk. It is probable that some of the localities referred to the 



* A single branching form, the G. milesi, has been published in the Geological Report 

 of Vermont. The specimenewaa found in a boulder of slate, but it is probably of the 

 Quebec group. 



