CHAPTER 2. THE STORY OF OHIO'S ROCKS 



GENERAL. When we look at Ohio today and see all about us the achievements of man, 

 the cities, the broad acres of farms and orchards, we take pride in the prosperity of our state 

 and in the industry and ingenuity which made them possible. The historians tell us that Ohio 

 was once densely covered with forest except for a few open areas and that the state was a happy 

 hunting ground for a sparse population of Indians. But, before that, what was Ohio like? It is 

 to geology that we must turn for an account of Ohio's distant past. For these events we cannot 

 rely on written documents nor even on the remains of man, his weapons, and tools. We must 

 turn to the record of the rocks, written in layers of mud and sand which consolidated into shale, 

 limestone, and sandstone, and the fossils that they contain. They permit us to decipher, at 

 least in their broader outlines, the events that preceded the coming of man in Ohio and to trace 

 the history of the land from the very beginning of the earth to the present. 



The Geologic Time Table 



ERA 



CENOZOIC 



MESOZOIC 



PALEOZOIC 



PRE -CAMBRIAN 



PERIOD 



PLEISTOCENE 



1,000,000 years ago 

 TERTIARY 



55 million years ago 

 CRETACEOUS 



JURASSIC 



TRIASSIC 

 161 million years ago 

 PERMIAN 



Not found 

 in 

 Ohio 



PENNSYLVANIAN 



MISSISSIPPIAN 



DEVONIAN 



SILURIAN 



ORDOVICIAN 



CAMBRIAN 



475 million years ago — — 

 Subdivisions not established. 



Fig. 4 

 8 



