94 SIXTEENTH REPORT ON THE CABINET OF NAT. HISTORY. 



Erie; but this is not true in regard to the species of the higher 

 beds of the group. 



The plants of the Genesee slate and Portage group, recognized 

 in the central part of the State, extend to Lake Erie, and again 

 appear in the same position at Kettle point on Lake Huron. 



In the Chemung group, remains of plants everywhere occur in 

 the eastern portions of the State, becoming more rare in the 

 central part, and extremely rare in all the localities examined in 

 the southwestern counties. In the western localities, we everv- 

 where find the drifted or floated fragments, spread in thin laminse 

 over the layers of shaly sandstone, and the recognizable species 

 are fragmentary. This gradual diminution in the frequency of 

 these remains, and in the size of the fragments, leaves no room 

 to misapprehend the then existing conditions. Almost always 

 mingled in the same beds with marine organic remains, we infer 

 that tliay are often drifted specimens which have floated from the 

 place of their original growth. 



This well-marked condition, over an extent of three hundred 

 miles, clearly foreshadows a limit to the extension of plant re- 

 mains ; for under the same conditions, they cannot continue in- 

 definitely to the westward. . 



In the general term Devonian, we have recognized in New- York 

 at least four distinct epochs : the first consisting of the Cauda- 

 galli and Schoharie grits, and the Upper Helderberg limestones; 

 the second, the Marcellus shale and Hamilton group ; the third, 

 the Portage group ; and the fourth, the Chemung group. In the 

 far eastern localities, these subdivisions have not yet been ob- 

 served ; a fact which might be inferred from the similarity of the 

 material in the easterly extension of the three higher groups of 

 the New-York sedimentary formations. 



Although the conditions described are unfavorable to a strict 

 determination of geological limitations of species, I believe we 

 may still recognize three epochs in the Flora. Certain species are 

 confined to the Hamilton group ; while the Genesee slate and 

 Portage group give another series, and the Chemung group a 

 third. It is probable that when the limits shall be properly de- 

 termined, no more than one or two species will be found to range 

 beyond the single epoch. 



With the exception of the partial and obscure formation of the 

 Cauda-galli grit, the lower members of the Devonian system in 

 New- York, and to the westward, are for the most part marine 

 calcareous accumulations, characterized by certain fossils of ma- 



