GEOLOGY AND PALEONTOLOGY OF THE SCHOHARIE VALLEY 177 



the progressive westward overlapping of higher and higher Oris- 

 kany strata, the highest of which only, with its modified fauna, 

 reached this western region, long after the normal Oriskany 

 fauna had died out in eastern New York. Clarke 1 has described 

 the character of these deposits across Xew York State as lenses 

 of sand spread upon a comparatively even sea floor. In one lens, 

 the thickness reached is 18 feet, in other localities the formation 

 has thinned away altogether. This, as Clarke has shown, is in con- 

 formity with the characteristics of an advancing shore line. The 

 absence of upper Oriskany beds with a fauna corresponding to 

 that of the Decewville beds in the east, is more difficult to ex- 

 plain, unless we regard the Esopus shales as their stratic equiva- 

 lents, though representing an Appalachian type of deposit in 

 which the Oriskany fauna could not exist. The Decewville and 

 Esopus deposits would thus represent two distinct subprovinces 

 of the late Oriskany sea, the first a deeper water and the second a 

 shallow water type of deposit. If we accept this as the true 

 explanation we can understand the absence of the Esopus 

 throughout the west, which otherwise is explainable only by an 

 hiatus. It also does away with the necessity of supposing that 

 there is an unrepresented hiatus between the Oriskany and the 

 Esopus in the Schoharie and Helderberg regions which marks 

 the time during which the Decewville beds were laid down. There 

 certainly is no evidence of an erosion interval between the Oris- 

 kany and Esopus of this region, for everywhere the surface of the 

 Oriskany is formed by the same hard quartzite. Nor is there 

 any apparent evidence of a break between the Oriskany and Onon- 

 daga in the Cayuga Ont. region; the association of the two faunas 

 is so intimate. We might of course assume that ihe Oriskany 

 faunas (i. e. of Becraft Mt, Schoharie and Decewville) were con- 

 temporaneous, but flourished in separate provinces of the interior 

 sea. In that case the absence of the Esopus from the western 

 region must be explained by assuming a stratic unconformity 

 between the Decewville-Oriskany and Onondaga. On the whole 



l Amer. Ass. Adv. Sci. Proc. 49:188. 



