374 Frank Carney 



For many miles off the eastern coast of the southern Atlantic 

 States the ocean is very shallow. A relatively slight upward 

 movement of this part of the contincuit, or a correspond- 

 ing withdrawal of the ocean, would add to the area of North 

 America. This added belt would be called a ''coastal plain." 

 Continents often grow thus, taking from the shallower parts of 

 the oceans. 



The Cincinnati arch. Towai'ds the close of the Paleozoic era 

 the sea withdrew fhudly from the region of Ohio. Before that 

 time, only a small jiart of the state's area was above sea-level; 

 in the southwestern corner, about C-inciiuiati, is the oldest land 

 in Ohio. Long l)efoi'e the close of the Paleozoic era, a dynamic 

 movement gradually i)roduced an arch, raishig from the surround- 

 ing sea a long peninsula-like strip. This has been termed by 

 students the "Cincinnati arch," and it is veiy typical of the oro- 

 gra])hic movements associated with the growth of continents. 



Just why certain areas near the continent borders are moved 

 <lifferentially, or bent into arches, is not clear. Some hold that 

 it is due to the une(iual distribution of sediment from the contig- 

 uous lands. If the products of disintegration were evenly 

 spj'ead into the oceans, it is urged, we would not have the irreg- 

 ular oscillations, but where a narrow ti'act is thus overloaded the 

 rocks beneath are compressed accordingly and an arching of 

 neighboi'ing rocks is produced. WIuml two such overloaded 

 areas arc; not far apart, tlu; intervening belt may be bent ui)ward, 

 as illustrated in the Cincinnati area. 



Students determine^ the a])pi'oximate time when such a move- 

 ment occui'i'ed by a study of the rocks involved. In the case at 

 hand tli(> disturbed rocks sh(jw a maximum movement near the 

 southwTst coriuM- of the state, only dimiiiishuig northward; one 

 effect of this arcdiing and the resultant stream erosion may be 

 seen today in th(^ scattered limestone islands about Sandusky. 

 The strata di]) dowuwai'd on either side of the axis of this uplift. 

 Along the axis the older rocks are found nearer the surface. Pur- 

 thermore, along this axis weathering and stream erosion have 

 })e(Mi most active; also th(> last sedinuMits de])osite(l before the 

 movement began are ui)])(M'm()st, and dij) either way from the 

 axis. Sinc(^ along the borders of this arched area, the rocks are 

 nuich younger than any found on its toji, it is inferred that the 

 arching conunenced before these younger sediments were depos- 



