Geography of Ohio 379 



Permian. The exact distribution of Permian formation has 

 not been worked out in Ohio. Their existence north of the Ohio 

 river has been estabhshed, and the State Geological Survey is now 

 engaged in mapping the Permian rocks. For this reason the 

 state map makes no mention of this period. 



IN GENERAL ON GEOLOGIC PROCESSES 



The tearing down of old rocks and building their products up 

 again into new ones, as above described, is a relatively simple 

 process. But simplicity of action is not general in earth-history. 

 Conditions appear constant only because of our limited period 

 of observation. Perhaps in no other science is there less compre- 

 hensiveness than in Geology, not only because much of its data 

 does not admit of close study, but also because this data, to be 

 correctly interpreted, mus't be observed through periods involving 

 the lives of many generations. It is for this reason, that we have 

 so few geologic activities standardized. The mountains are 

 not stable, nor are the seas confined; the former wear away, the 

 latter deepen and shallow. When there is stability in the one 

 and mobility in the other, the line of contact on which both are 

 measured shifts accordingly. So it may be impossible to say 

 whether a certain change in altitude represents an upward or a 

 downward movement of the land, or an extension or withdrawal 

 of the seas. Either movement on the part of either body intro- 

 duces the appearance of the opposite movement on the part of 

 the other. If the sea withdraws, the area of the land increases; 

 if the land subsides, the sea appears to be extending. But these 

 shifts which vary altitude are only one manifestation of the in- 

 constancy of our land and water bodies. Instead of being able to 

 interpret these movements as due either to a definite uplift or 

 depression of land, or to the extension or retreat of waters, closer 

 study usually shows that there has been a differential movement, 

 indicated here by a certain rate of uplift or retreat, and there 

 by a different rate. While the full value of these movements in 

 time past may never be accurately estimated, it is, however, a 

 satisfaction to know that the students of later generations will 

 have accumulated data on which more satisfactory conclusions 

 may then be based. 



