202 NEW YORK STATE MUSEUM 



fish plates (Dinichthys, Pristacanthus) and scales (Palaeoniscus, Acanthodes) 

 and though the calc nodules and more persistent calc sheets contain inverte- 

 brates (goniatites, Pterochaenia, Paracardium, Styliolina) we shall presently 

 observe that the latter have been measurably effected by eastward currents 

 from the open sea. 



For the most part, however, the deposits of this Portage sea along its 

 northern extent were in shallower water and constituted of clay muds 

 commingled with sand, more of the former than of the latter in western 

 New York, more sand than mud nearer the emerging and encroaching coast 

 farther to the east. It was a period of active stream erosion on Portage 

 land, for the sand and mud swept out to sea by river and undertow reached 

 a notable thickness, fully 1300 feet where thickest and sandiest (Chenango 

 county), 1200 feet on the Genesee river, where both muds and sands abound, 

 but much less on the shore of Lake Erie. 1 It was therefore a time of exten- 

 sive reduction of elevated continental areas, a time of shifting shore lines 

 and sand bars, of encroachment of littoral deposits on the deeper water and 

 of the foul, black muds of the depths on the sands. It is to the gray muds 

 that the fauna specially appertains, and, though ranging through the higher 

 sandstones of the sections, yet its development is always more sparse in such 

 deposits. It is likewise the sands that carry for the most part abundant 

 traces of terrestrial vegetation and that show the trails of crustaceans 

 and annelids and the rills and ripple marks of the beaches. The eventual 

 conditions of rapid erosion manifested during later Portage time and the 

 rapid reduction of the Portage highlands (Appalacliia to the south ; 

 Lanrentia to the north) were continued in time beyond the Portage with 

 which we are not now directly concerned. The deep water conditions repre- 

 sented by the black shale deposits and on which the sands encroached were 

 continuously prevalent toward the west. In Erie county it is not easy nor 

 is it at all important to distinguish between the black shales commonly 

 referred to the Genesee and those which are palpably equivalent to the 

 lower of two strongly bituminous shale bands eastward in Ontario county; 



'See the comparative sections given on p. 212 et seq. 



