Geography of Ohio 383 



Limestones are soluble, hence are readily affected b\ surface 

 weathering and ground water. Clastic rocks containing a soluble 

 cement yield rapidly to the same agencies. Formations made up 

 largely of either of these types of rock go to pieces much more 

 quickly than do rocks that contain no soluble constituents. 



Sometimes the rock has a simple structure; at other times, 

 complex; the simplest structure is an approximation to the hori- 

 zontal position, the original attitude of most sedimentary forma- 

 tions ; the more complex attitudes are found in mountain areas 

 like the Appalachians and the Swiss Alps; jointing and faulting 

 may introduce further complexit}' of attitude. ^ATien the rocks 

 have been highly folded, some of the formations being harder 

 than others, the structural valleys, and the inequalities resulting 

 from differential weathering, give the country a very irregular 

 surface, as illustrated in parts of Pennsylvania. 



Massive beds of rock are more resistant than thin layers. Occa- 

 sionally, sedimentary beds may be heavy, but massiveness is 

 usually associated with igneous rocks. 



Furthermore, if the rocks are loose in texture and are fairly 

 homogeneous throughout the district, the stage of strong relief 

 will not endure long; even when such formations have been folded 

 and faulted, but not to the extent of disclosing rocks which differ 

 much in texture and structure, the result t\'ill be the same. When 

 thick hard horizons alternate with less resistant strata, irregular 

 topography prevails much longer; the more resistant a given for- 

 mation is, the longer it withstands weathering, and stamps itself 

 on the topography; even in the absence of crustal deformation, 

 this arrangement of rocks will give some relief, but when the 

 strata have been folded, the surface irregularity is correspondingly 

 greater. Since in Ohio, omitting an area in the southwestern 

 part of the state, all of our formations have a general dip to the 

 south and east, the relief quite accurately reflects the rock texture 

 and structure. 



If one starts from Toledo and crosses the state directly to Park- 

 ersburg, W. Va., he passes over the outcropping edges of most 

 of the rock formations in Ohio. The first part of his journey is 

 over limestone horizons; this is followed by a belt in which shale 

 outcrops ; thus far, the route covers a region of slight relief, largely 

 because the limestone and shale have weathered uniformly. Next 

 he enters a belt of clastic sediments, consisting chiefly of sandy 



