GEOLOGY OF OHIO. 



CHAPTER I. 



GEOLOGICAL SCALE AND GEOLOGICAL STRUCTURE OF 



OHIO. 



By Prof. Edward Orton. 



Owing to the mode of distribution of the volumes of the Ohio Geo- 

 logical Reports, viz: through the members of the successive legislatures 

 that order the publication of the successive volumes, it becomes neces- 

 sary to introduce each volume as it appears, with a brief review of the 

 geological column of the state, in order to make it certain that the state- 

 ments which are to follow will be properly understood by those into 

 whose hands the volume may fall. It is never safe to assume that those 

 who receive one volume have any knowledge of or any means of obtain- 

 ing any other volume of the series. 



The geological scale of Ohio comprises strata, named in ascending 

 order, of Lower Silurian, Upper Silurian, Devonian, Sub-carboniferous 

 and Carboniferous age, and also a series of deposits of the Glacial period. 

 The principal divisions are shown in the following table. The thickness 

 that is assigned to each of the elements is not necessarily the average 

 thickness of the various exposures.' In some cases the more common 

 measure is given; in others it is counted better to indicate the thickness 

 of some of the best known exposures. . In the text, the limits of each 

 formation will be more definitely stated: 



The geological order herewith described is further represented in the 

 accompanying diagram. A brief review> of each of these divisions will 

 be made in the succeeding pages of the present chapter. 



