THE GEOLOGIC DEVELOPMENT OF OHIO 

 Feank Carney 



Introduction 365 



Geologic time 



River sediments 



Ocean sediments 

 The origin of rocks 368 



Nebular hypothesis 



Planetesimal hypothesis 



Age of weathering processes 



First stage in rock-making 



Metamorphism 



Clastic and organic rocks 



Rocks precipitated from solution 

 The growth of land areas 373 



The Cincinnati arch 



The Appalachian mountain-making movement 



The Allegheny plateau 



Relief and glaciation 



Periods of geologic time represented in Ohio 376 



In general on geologic processes 379 



INTRODUCTION 



The surface features of any region pertain to its geography ; 

 the underlying rocks contain its geology, and embody a composite 

 of its past geographies. To-day's geography, then, will become 

 a page in the geology of the future. 



Geologic time. That the rocks may be analytically studied, 

 men have grouped them into eras and smaller divisions. The 

 basis on which the rocks have been thus classified is chiefly their 

 content of fossils, though geographic changes are important. 

 The oldest rocks are said to be without organisms; from that early 

 era to the present, the gradual development of species, and the 

 gradual increase in biologic complexity, has led to the naming of 

 the succeeding eras. The better known eras are divided into 

 periods, representing either a striking difference in their fauna, or 

 an unconformable relationship to the strata of the preceding 

 period : 



365 



