276 GEOLOGY OF OHIO. 



where the thickness is greatest. It tends to become impure and slaty. 

 Occasionally part of it becomes cannel coal of indifferent grade. 



While there is a large body of fuel to be found on this horizon, it 

 does not seem probable that it can compete in the markets of our day 

 with the seams that are now being mined. It does not, however, follow 

 that it will remain without value for all the future. When the time 

 comes, as it must come at no distant day, in which different grades of 

 coal can be offered in market at prices corresponding to their intrinsic 

 value, the Upper Mercer coal will then find its proper recognition. 



The Tionesta Coal. — Some doubt has been expressed as to the exis- 

 tence of a coal seam sufficiently persistent to deserve to be. included in 

 our list between the Upper Mercer and the Brookville coals. It must be 

 acknowledged that the question as to these lower coals can be studied 

 further with profit. There are, however, a few sections in Ohio, ar 

 shown in Volume V, in which a coal seam of thickness sufficient to jus- 

 tify mining, at least in a small way, is found about equidistant betweei? 

 the Upper Mercer coal and the seam which underlies the Putnam Hill lime- 

 stone. The latter is counted in Volume V as the Brookville coal, or the 

 representative of the first seam of the Lower Coal measures proper. The 

 question of identification, hower, extends to this last named seam, as 

 well as to the one below it. There is more stratigraphical than economic 

 importance, in the questions so far as Ohio is concerned, and since no 

 new facts have recently been brought to light upon the section involved, 

 the question must be left here unsettled, as it was left in Volume V. 



SECTION II. 

 The Coal Seams of the Lower Coal Measures. 



The division which we now reach in our review, is by all means the 

 most important division of the Carboniferous system in Ohio. We find 

 here not only a larger number of coal seams that justify mining, than in 

 any other division, but we find associated with these coal seams the most 

 valuable beds of fire clay of our entire series. The only limestone for- 

 mation of the Coal Measures that is found reliable in a large way foi 

 lime-burning and for furnace flux is also included in the same division, 

 viz., the Ferriferous limestone. To this list there should be added num- 

 erous beds of iron ore that were counted of considerable value a few 

 years since, but which have lost their economic importance, in great part, 

 since the development of the iron ore fields of Michigan, Wisconsin and 

 Minnesota. 



The coal seams of the Lower Cbal Measures in Ohio are six in num- 

 ber. They are named below in decending order : 



6. Upper Freeport coal. 

 5. Lower Freeport coal. 

 4. Middle Kittanning coal. 



