378 Frank Carney 



a very irregular surface distribution. Kelley's island and the 

 eastern end of Marblehead peninsula consist of Devonian forma- 

 tions, as does also the northwest corner of the state, omitting 

 Williams county and a portion of the western end of Fulton 

 county. From Sandusky eastward, the Devonian occupies 

 a narrow strip bordering the lake, narrow as far as the meridian 

 of Unionville, Lake county; east of this meridian, the Devonian 

 outcrop broadens southward into Trumbull county. 



Mississippian. In the northwest corner of the state, the De- 

 vonian formations border an area comprising all of Williams county 

 and part of Fulton; the rocks of this area are mapped as probably 

 of Mississippian age. The principal area of the Mississippian 

 outcrops extends northward from the Ohio river; this area on the 

 west has a fairly uniform boundary with the Devonian on the 

 west; but on the east, its contact with the later formations is 

 very irregular, the irregularity increasmg to the south. The 

 channel of the Ohio river shows Mississippian formations from 

 the Devonian outcrop in southwestern Scioto county eastward 

 to the vicinity of Ironton. Along the east and south-flowing 

 streams, including the Hocking, Licking, Mohican, Killbuck 

 and Cuyahoga rivers, outcrops of the Mississippian reach into 

 the territorj^ of the next later period. East of the Cuyahoga 

 valley the Missippian formations meet the Devonian in a very 

 regular line of contact, but occupy a relatively narrow surface 

 area as far as the meridian of ITnionville; beyond this meridian 

 in Trumbull county, the Mississippian area broadens almost to 

 the north-south width of the county. The valley of the Mahoning 

 cuts into the Mississippian rocks as far east as Youngstcvvn. 

 From Youngstown northward, the contact with the rocks of 

 the next later period is quite irregular. 



Pennsylvanian. Nearly all the remainder of the state is occu- 

 pied by the outcrops of this period; in this area is found the 

 most broken topography of Ohio, and the greatest variation in 

 altitude. The Pennsylvanian rocks approach Lake Erie nearest 

 in Geauga county. The boundaries of the different formations 

 of the Pennsylvanian rocks are extremely irregular. In no por- 

 tion of the state are the streams more numerous. This active 

 river erosion has produced the irregular distribution of the Penn- 

 sylvanian formation. 



