PHYSICAL AND FAUNAL EVOLUTION 



83 



the Virginia, western Tennessee, and Oklahoma occurrence of this 

 series beginning with beds carrying a New Scotland fauna.' 



The emergence of the North American continent at the end of 

 Siluric time was accompanied by the first pronounced doming of the 

 Cincinnati region and basining of the Michigan area. Local oscil- 

 lations seem to have preceded this, but the first great movement 

 apparently did not occur until the end of the Siluric. Between the 

 Michigan basin and the Cincinnati dome were formed the Wabash 

 anticline and the minor folds of Michigan, Ohio, and Canada. When 

 these regions were again wholly submerged in Mid-Devonic time, 

 the deposits of this later epoch came to rest on the beveled surfaces 

 of various Siluric members (see Fig. 11). A subsequent movement 



Northern Michigan 



Southern Michigan 



Northern Ohio 



Central Ohio 



Southern Ohio 



Fig. II. — Section from northern Michigan to southern Ohio, showing the rela- 

 tionship of the Middle Devonic to the Siluric and of the Upper to the Middle Devonic. 

 O = Olantangy shale. 



in the same direction, at the end of Paleozoic time, threw the later 

 beds into similar folds, while emphasizing those of the earlier series. 

 A marked hiatus occurs between the Helderbergian and Oris- 

 kanian. The former series is beveled, so that the Oriskany comes to 

 rest, as it extends westward, upon lower and lower members of the 

 Helderbergian, and finally upon the Manlius, and still farther west 

 upon the Akron dolomite (Cobleskill) . This beveling is in part due 

 to retreatal "off-lap" but also to extensive erosion which indicates 

 a time-period of some magnitude for the Oriskany. The deposi- 

 tional equivalent of this hiatus is found in the Gaspe region of Canada, 

 where 550 feet of Oriskanian (Grand Greve limestone) follows 



I See Grabau, Bull. 92, New York State Museum. 



