84 AMADEUS W. GRABAU 



1,200 feet of Helderbergian (St. Albans and Bon Ami limestones), 

 the succession being a conformable one.' 



The Oriskany of the United States is mostly a sandstone, often 

 of pure quartz grains, at other times calcareous. The source of the 

 sandstone is to be sought in the sandstones of the eastern extension of 

 the Siluric and Ordovicic formations, and perhaps in the exposures of 

 the St. Peters and the Sylvania. It seems most likely that the distri- 

 bution of the sand over eastern North America was largely effected by 

 wind, during the long period of erosion preceding the submergence 

 of the continent. On the westward extension of the Oriskany sea 

 these accumulated sands were reworked and were transformed into 

 the fossiliferous marine sands which they are found to be today. 

 In the east, after a short period of sedimentation, an extensive accumu- 

 lation of black muds occurred, forming the Esopus-Schoharie shale 

 series. This has its greatest thickness at Port Jervis, whence it 

 thins away in all directions, apparently by overlap. Since the source 

 of the material was clearly in the east, and the overlap is toward 

 the west, north, and south, the formation must be a subaerial fan. 

 This is further indicated by the general absence of fossils, except for 

 occasional intercalations, such as would be expected in a fan of this 

 kind, probably rising but slightly above the level of the shallow Oris- 

 kany sea. The continuance of the Oriskany invasion is found in 

 the spread of the limestone with the Schoharie fauna and the succeed- 

 ing Onondaga submergence. During Onondaga and Hamilton time, 

 continuous deposition and spreading of the seas went on, but at the 

 close of the Middle Devonic, renewed emergence affected most of 

 southern and southeastern United States, accompanied by erosion. 

 This again was followed by the slow resubmergence, which commenced 

 from the north and slowly advanced southward and eastward. The 

 basal member of this transgressing series is the black shale, which, 

 in northern Michigan, is of Lower Devonic (Genesee?) age, but 

 becomes of later and later age southward, at the same time resting 

 always on lower strata. Thus late Upper Devonic (Portage) black 

 shale rests on Lower Hamilton in southern Michigan and northern 

 Ohio; still later beds (Chemung) on the Onondaga (Columbus) 



I See J. M. Clarke, " Early Devonic History of New York and Eastern North 

 America," New York State Museum Memoir g, 1908. 



