128 HISTORICAL GEOLOGY 



coarse, clastic sediments argues for considerable land rejuvenation, 

 or much more rapid erosion, or both. The sediments are of distinctly 

 shallow-water character, and the fossils show the fauna to have 

 been suited to such conditions. The fossils are remarkably similar 

 to those of the same age (Coblenzian) in Europe from which region 

 they appear to have migrated. "The evidence then is fairly 

 conclusive that during the period represented by the Coblenzian 

 Oriskany, the arenaceous epicontinental sediment was the ground 

 traversed by the Coblenz fauna westward along the North Atlantic 

 continent" (J. M. Clarke). In other words, there must have been 

 a land connection between Europe and North America. 



Middle Devonian. — During Ulsterian time (neglecting the 

 slight deposition of Schoharie grit in eastern New York) important 

 geographic changes took place. The Appalachian Basin from 

 Pennsylvania southward was raised into land, but the sea con- 

 tinued from eastern New York and Pennsylvania across the Upper 

 Mississippi Basin to northern Michigan and southern Illinois, 

 except probably around the Cincinnati anticline area. Much of 

 New Brunswick and the region at the southern end of Hudson Bay 

 were submerged, as well as the Rocky Mountain district from 

 Alaska to western Colorado, northern Arizona, and Nevada. 

 Marine waters covered the areas much as shown on the map 

 (Fig. 70) except for the absence of the sea from the northern Ap- 

 palachian district and the large area from the Mississippi River to 

 the Rocky Mountains. This was the great Onondaga sea, which 

 must have been mostly clear, shallow, and comparatively warm as 

 indicated by the widespread accumulation of largely coralline 

 limestone already mentioned. Evidently there were no rapidly 

 eroding land areas. 



Late middle Devonian (Erian) time witnessed another impor- 

 tant physical change probably due to a very considerable rejuvena- 

 tion of northern Appalachia, resulting in renewed erosion and 

 deposition of vast quantities of muds in the eastern part of the 

 interior sea. These muds are now hardened and called the Mar- 

 cellus and Hamilton shales. Farther westward in the Mississippi 

 Basin, however, much limestone still formed in the clearer sea. 

 The relations of land and water during this (Erian) time are de- 

 picted on the paleogeographic map (Fig. 70). One feature to be 

 especially noted is the long, narrow, land-bridge from Wisconsin 

 to Texas, separating the eastern from the western interior seas. 



