DESCRIPTION OF THE FORMATIONS. F a . 57 



red shale. The only other species named by Prof. Hall is 

 a eurgpterus from Williamsville, Erie county, which cannot 

 be from the red shale, as that bed is said not to be found 

 west of the Genessee. Its indications are of Lower Helder- 

 berg affinities, in this respect agreeing with those of Leper- 

 dltla alta and Beyrichia notata above-mentioned. 



Onondaga Bridgeport sandstone. 



In the mass of red shales comprising the lower part of the 

 Onondaga lies a bed of hard flinty sandstone deserving some 

 notice. Its occurrence in so thick a mass of shale is very 

 surprising as is also its small extent. It is merely a local 

 patch of quartz sand thinning out in all directions from a 

 center near Bridgeport, whence the name. 



It is difficult to account for the presence of so large a mass 

 of this material so deposited. From what source can it 

 have been derived ? How was so limited a mass of sand 

 transferred or deposited in a thick mass of red shale with- 

 out connection with any other similar deposit ? A similar 

 bed, perhaps the same, may be seen in the red shale near 

 Bistline's mill, in Madison township. It is only two feet 

 thick. (See report on Madison township.) No sign of any 

 such bed can be seen at other exposures of the red shale at 

 intervening points, as at Waggoner's mill, where an almost 

 complete section can be got. 



The two exposures of the Bridgeport sandstone, at which 

 it is best shown, are near Bridgeport, on the bank of Sher- 

 man's creek and near Mr. Egolf s mill, in Kennedy's val- 

 ley. For details of these see report on Tyrone township. 



The occurrence of these two beds at so distant places with 

 no signs of similar beds at intervening stations, suggests the 

 possibility of a shallowing of this part of the ancient ocean 

 over a considerable area, producing sand-banks on which 

 the heavier material was accumulated, while the finer parts 

 were swept away. This, if true, must be accompanied by a 

 less thickness of the red shale under and near the sandstone 

 deposits. Of this, however, I have found no evidence. The 

 only place where an opportunity of making such a meas- 

 urement has offered itself being in Madison township, near 



