40 Cincinnati Society of Natural History. 



Silurian, they belong. Cumings considers that the move- 

 nients of the Richmond and Medina stages were related, 

 and that the Richmond is equivalent to a part of the Medina. 

 Bassler places the Richmond formation in the Silurian 

 system, evidently in accordance with this idea of its con- 

 temporaneity with the eastern formations. 



2. Silurian period. — That an emergence of the Cincinnati 

 anticline occurred late in the Richmond or early in the 

 Silurian is further indicated b}'' the different nature of the 

 later Silurian formations to the east and west of the anti- 

 cline. The Clinton of Ohio and Indiana is very similar 

 faunally and lithologically''' thus precluding the existence 

 of any extensive land mass at that time, but the Waldron 

 of Indiana* and Tennessee is not represented by any similar 

 formation in the area to the east of the anticline, which 

 might be interpreted by assuming that a land barrier 

 existed between these two basins. It is probable that dur- 

 ing the subsequent periods of the Paleozoic, this area was 

 generally above the sea, but was low lying and suffered 

 little erosion. 



B. Post-Paleozoic Time 



At the close of the Paleozoic, all the eastern interior was 

 raised above sea level, and there was extensive deformation 

 in what is now the Appalachian Mountain region. Long 

 continued erosion then followed resulting in the formation 

 of an extensive peneplain in Cretaceous time. Evidence of 

 this peneplain still remains in the mountain regions, but has 

 been obliterated from the great interior areas underlain by 

 less resistant rocks, where it was no doubt also formed. 

 After the formation of the Cretaceous peneplain, there was 

 an uplift which inaugurated a second great period of erosion, 

 again resulting in the formation of a peneplain in Tertiary 



*Cunimgs: Ind. Dept. Geol. Nat. Res., 32nd Ann. Rep., 1907, p. 687. 



tBassler: Proc. U. S. Nat. Mus., xxxix, 1911, pp. 509, 517; U. S. Nat. Mus. Bull. 92, 1915, 

 vol. 2, pi. 3. 



IFoerste: Amer. Jour. Sci., vol. 18, 1904, pp. 321-342. 



jKindle and Barnett: Ind. Dept. Geol. Nat. Res., 33rd Ann. Rep., 1908, p. 401. 



