Geography of Ohio 375 



ited. Accordingly, the beginning of the uphft movement has 

 been definitely associated with the latter part of the Ordovician 

 period. 



Appalachian niountain-niakiiuj fnovement. For a long time 

 after the development of the Cincinnati arch, the Ohio region 

 was almost continuously a part of the sea. In addition to the 

 arched area, lands exposed to weathering existed to the north, 

 and farther away to the east. From these sources, products 

 of weathering were being transported, gradually making more 

 and more shallow tlu^ sea over this rc^gion. The great dynamic 

 movement that produced the iVppahichian mountains commencetl 

 in the Permian, the closing period of the Paleozoic era. This 

 folding ])robably began in the eastern section of the northern 

 Appalachians, proceeding westward and southward. The young- 

 est sediments found in Ohio belong to the Permian. It is pos- 

 sible that sedimentation may have continued after that period 

 in parts of our area; if so, such deposits have been com])letely 

 removed, or have never been located by geologists. 



Since the Pei-niian, then, the normal agents of weathering, 

 which we see all about us to-day, have been acting on the rocks 

 of oui- state, sometimes subdued, at others vigorous. At inter- 

 vals the rivers have been building flood plains, as their velocities 

 lessened; again, because of a differential movement, or because 

 of an u])lift, the invigorated streams commenced to erode their 

 beds and cany away waste products. Tjater, all these ])rocesses 

 were checked in about half the area of Ohio by a sheet of ice (p. 

 185). 



The Allegheny plateau. The western slope of the Allegheny 

 plateau ext(Mids diagonally across the state from northeast to 

 southwest. This plateau, I'anging in altitude up to thirteen or 

 fourteen, hundred feet, is genetically associated with the same 

 movement that produced the Api)alachian mountains. The Ohio 

 river and its tributaries have in a measure severed this part of 

 the uplifted regicm from th(^ moi-e elevated section to th(^ east; 

 the Scioto, of its several tributaries, occupies the greatest gap in 

 the plateau. Not only is this section elevated, but closer study 

 of the rock structures betrays many folds and flexures also, 

 consisthig of slight anticlines and synclines. The i-ocks con.cerned 

 have a prevailing dip to the south and east. They consist of 

 clastic sediments in the main, mostlj^ sandstone and conglomerates ; 



