Remarks upon Sedimentation in t/ie Cincinnati Group. 35 



Geological Survey of Ohio, refers to the various sorts of sediment 

 forming the strata of the Lower and Upper Silurian and the Devonian. 

 He says that the Potsdam sandstone, for example, was laid down 

 upon a beach, and is " the first product of the invasion of the Eozoic 

 continent by the ancient ocean. "* That the Calciferous sand-rock, 

 lying next above, may be considered as formed of sediments thrown 

 down in deeper water, and as the second product of the invasion 

 by the sea ; that the Trenton, next above, has resulted from the 

 accumulation of organic matter at the bottom of a great ocean; and 

 that finally the Hudson River Group, including the Cincinnati rocks, 

 represents an epoch of retreating and shallowing seas and of a rising 

 continent. 



Everything that is known of the organic remains from the various 

 formations points to the truth of this idea. The evidence of the inor- 

 ganic remains testifies in a similar way. The presence of beaches at 

 two and probably three horizons in the Cincinnati Group indicates 

 two or three periods of elevation and subsequent depression. Eleva- 

 tion enough to bring the forming rocks to the surface for a sufficient 

 length of time to allow of the formation and preservation of tracks, 

 trails, etc., and depression enough to permit the laying down, in one 

 case, of three hundred feet of shales and limestones, and in the other 

 of an additional two hundred feet or more. 



It is interesting to note, as was also pointed out by Dr. Newberry, 

 that a cycle of events occurred in the Upper Silurian similar to that of 

 the Lower. The Oneida conglomerate and the Medina sandstone 

 correspond to the Potsdam sandstone, the Clinton to the Calcifer- 

 ous, the Niagara to the Trenton and the Lower Helderberg to the 

 Hudson Group, or the Lorraine shales. In addition, however, 

 there was the Salina, or Onondaga Salt Group, which as T. Sterry 

 Hunt suggests, probably resulted from the evaporation of the sea- 

 water from shallow basins partly enclosed by land. It would be inter- 

 esting to know whether, in addition to the similarity of deposits of 

 sediment, the Lower Helderberg Group will present evidences of suc- 

 cessive beaches at several horizons, such as have been shown to exist 

 in the Cincinnati Group. We know that in New York there are sev- 

 eral successive beds characterized by more or less distinct faunas, and 

 these certainly indicate varying conditions of deposit. Furthermore, 

 inasmuch as the Hamilton Group closes a circle of deposition during 

 the Devonian period, might we not look for similar oscillations of level 



*Geol. of Ohio, Vol. I., p. 58. 



