oped and most persistent horizons, however, are the Lower and Upper 

 Mercer limestones with their accompanying iron ores; these members, 

 especially the Lower Mercer, are found in every county where they 

 may be expected, and form datum planes of extreme importance for 

 determining the stratigraphic relations of the overlying and under- 

 lying formations. 



Economically the Pottsville formation is of considerable value, 

 and it has added much to the natural resources and wealth of the 

 State. Most of the iron ores which have been worked for the purpose 

 of smelting in the old charcoal furnaces, particularly in Scioto, Lawrence, 

 Jackson, and Vinton counties, were from this formation. The Lower 

 and Upper Mercer ores especially are of sufficient thickness and are 

 high enough in iron content to be of some importance commercially. 

 However, they in no way rival the ores of the Lake Superior region, 

 and at the present time are used only to a very limited extent. The 

 coals are utilized mostly for local purposes, but a few beds, such as 

 the Sharon coal and particularly the Quakertown or No. 2 coal, have 

 been mined for commercial use for the past forty years and have been 

 important factors in the development of industry in southern Ohio. 

 In Jackson County, the Quakertown coal is of good quality and 

 thickness, and is responsible for the rapid growth of Jackson, Wellston, 

 and other towns in the mining district. Pottsville clays are also of 

 importance economically, and the Sciotoville clay has been used for 

 many years in Scioto and Jackson counties for the manufacture of 

 refractory wares, for which purpose it sets a standard of excellence. 



A study of the Pottsville fossils shows that with the exception 

 of the coal formations, the members are marine in origin for the most 

 part. The marine conditions which produced these members alter- 

 nated with the swamp conditions under which the coal was deposited. 

 During six periods marine conditions favored the deposition of lime- 

 stone, and the first six members of the series of limestones of the 

 Pennsylvanian system were laid down, namely the Lo well ville (Poverty 

 Run), Boggs, Lower Mercer, McArthur, and Black Flint members. 

 The marine sediments were deposited in shallow waters, and as they 

 grew in thickness the water level was approached until swamp condi- 

 tions, necessary for the formation of coal, were brought about. A 

 slow depression, however, successively brought the swamp conditions 

 to an end and shallow marine waters again occupied the region, and 

 another series of marine sediments was deposited. The slow, periodic 

 sinking of the region and the subsequent building up of the sea bottom 

 to the water level were necessary for the alternation of marine sedi- 

 ments and coals. 1 



In the following discussion the faunal horizons of the Pottsville 

 formation are treated successively, so as to show the stratigraphic 

 relations, character, and .extent of each of these strata. 



1 Stout, W., Manuscript on Clays in Ohio. 



