viii PREFACE. 



portance at a few points in the State, are not delineated, except in a single instance 

 on the present series of maps. These seams are four or five in number, and one of 

 them, viz., the Sharon coal (Coal No. 1 of Newberry), has been an important ele- 

 ment in our coal resources up to the present time. But all the known areas of it 

 are either already worked out or are rapidly approaching exhaustion. It could 

 answer no useful purpose to delineate the original boundaries of exhausted coal 

 fields, and the known portions of the seam that remain untouched would appear 

 insignificant if laid down by themselves. 



The Ouakertown coal (Coal No. 2 of Newbeny) attains considerable importance 

 in one district of the State, viz., in Jackson and Vinton counties. It is here known 

 as the Jackson Hill or Wellston seam. Its areas, at least as they were understood 

 two years ago, are indicated on Map No. 2, by a subordinate boundary. 



The remaining seams of this division, viz., the Mercer and Tionesta coals, are 

 nowhere of importance enough to justify their representation on our maps from an 

 economic point of view. 



The next great division, the Tower Coal Measures, constitutes the heart and 

 center of the Ohio Coal Field ; but the two lowermost seams of this series are too 

 inconstant to justify representation. In Stark county the Brookville seam, or the 

 coal under the Putnam Hill Limestone is locally mined, but such is its uncertainty 

 that no good purpose could be subserved by representing it much beyond its 

 present development. 



A similar state of things is found in the case of the Clarion coal in Vinton and 

 Jackson counties. This seam underlies the famous Ferriferous limestone and there 

 is a considerable territory in which it gives promise of being able to support min- 

 ing in the large wa}-, but it was feared that more harm than good would come by 

 representing it as present in unexplored areas in which while it is geologically due, 

 it has not been proved. The Kittanning coals, Lower and Middle, therefore, are the 

 first seams to which the mapping has been made to apply. Inasmuch as the upper 

 of these two seams, viz., the Middle Kittanning, is immensely the more important of 

 the two, its outcrops are the ones that are represented. But, as already noted else- 

 where, the lower seam is separated from it by so small a vertical interval that the 

 one boundary answers almost equally well for both. 



A similar state of things is found to hold in the case of the two Freeport seams, 

 Lower and Upper. The Upper, which is by far the steadier and more valuable seam, is 

 represented by a boundary, but whenever the Lower is present in the same areas, the 

 one boundary is generally sufficient for all practical guidance. It is to be carefully 

 noted by all who study the maps, that where the Kittanning and Freeport bound- 

 aries appear on the same maps, the boundaries of the former are in all cases to be 

 continued through the areas which are assigned to the Freeport coal. 



It would have been more satisfactory if each seam could have had a sheet to 

 itself, but the demands of economy in the accomplishment of our work, necessi- 

 tated the adoption of the present plan. 



The great Pittsburg seam as a matter of course, comes in for a boundary in our 

 maps, as does also another seam a hundred feet above it, which is well developed in 

 three or four counties in the very centre of our coal area. The latter is known in 

 Ohio geology as the Meigs Creek coal. Finalfy, on map No. 10, the collected areas 

 of the several seams are shown in their outcrops. 



In the representation of each seam, the object has been to delineate the boun- 

 daries of those portions of it that lie above the natural drainage, but far more care 

 has been takeniu running the outcrop or upper boundary than in running the lower, 

 for the reason that when this lower boundary occurs, the character of the territory 

 is already established, as certain to be within the recognized boundaries of the 

 seam. In the drainage boundary there are always enough points definitely located 

 to justify the position given to this line in a general way. 



