366 Frank Carney 



Cenozoic. 



Mesozoic. 



Present 



Pleistocene 



Pliocene 



Miocene 



Oligocene 



Eocene 



Cretaceous (Upper Cretaceous) 

 Comanchean (Lower Cretaceous) 

 Jurassic 

 Triassic 



Permian 



Pennsylvanian 



Mississippian 



Paleozoic .{ Devonian 



Silurian 



Ordovician 



Cambrian 



I Keweenawan 



J Upper Huronian (or Animikean) 



Proterozoic -, t\t-jji tt 



1 Middle Huronian 



\ Lower Huronian 

 Archeozoic Archean 



The consolidated rocks of Ohio belong entirely to the Paleo- 

 zoic era; resting upon these, is much unconsolidated rock material 

 belonging to the Pleistocene and Present periods of the Cenozoic 

 era. We have, then, no rocks that are geologically very old, nor 

 have we the hard and resistant rocks. The formations of the 

 earlier periods have undergone changes that make them less 

 easily disintegrated by agencies of weathering; they are uniformly 

 more dense than younger rocks. The formations of the early 

 eras are usually crystalline in structure, whereas sedimentary 

 rocks characterize the later eras. It is not improbable that many 

 of the crystalline rocks were originally sedimentary. 



River sediments. Since the rocks of Ohio are sedimentary, it 

 follows that they had their origin in the assembling of the weath- 

 ered products of older rocks. The rivers that to-day carry off 

 the products of weathering are depositing these products along 

 their courses and in the oceans; such deposits will in time form 

 sedimentary rocks. 



