x PREFACE. 



judgment; and so, also, will be the fixing of an average thickness of our seams in 

 the several fields. 



In making an approximate determination of our coal lands on this new basis, I 

 have, in the first place, assumed a total breadth of the coal-forming swamps of 

 twenty miles, measured from the average outermost outcrop of the seam, in the di- 

 rection of the greatest dip. This shows a somewhat larger area of the seam under 

 cover than above drainage. The coals would thus be followed down to a depth of 

 200 to 300 feet below the surface. It does not seem to me that the most sanguine 

 student of the facts would ask for a larger extension of any of our seams that have 

 been treated in this way, unless an exception be made for the Upper Freeport Coal. 

 The Freeport coals seem to have had a somewhat different history from that of the 

 earlier seams, and for them it is possible that the assigned limit wull sometimes be 

 too narrow 



The areas assigned to the Pittsburg coal are deduced rather from reported 

 occurrences of the seam in deep borings than from any theoretical views. 



In the second place, I have had the areas of the seams in question measured as 

 they f.re found above drainage or rather until they are fairly under final cover. The 

 boundaries on which this measurement depends are visible and unquestioned. 



With areas of coal seams computed in square miles, and with the thickness of 

 each estimated in feet, the problem of determining the quantity of coal in township- 

 count}- or state, becomes a simple one. The specific gravity of Ohio coals ranges 

 between 1.24 and 1.34. I have taken 1.28 as a fair average. On this basis a cubic 

 foot of coal weighs eighty pounds. An acre of coal one foot thick, yields about 

 1,750 tons, and a square mile 1,120,000 tons. 



The two Kittanning seams show, on the first basis a total area of 3,873 square 

 miles; on the second basis, of 1,847 miles. For the combined thickness of the two 

 seams calculated for this area, I count four feet a fair figure. The contents of the 

 field are, therefore, 17,350,000,000 tons, by the first computation and 8,274,000,000 by 

 the second. 



The Freeport coals show, on the first basis, an area of 3,149 square miles, and 

 1,285 miles by the second. I assume four and one-half feet for the total thickness 

 of this area. The original amount of Freeport Coals in Ohio, is, therefore, 15,880,- 

 000,000 tons by the first computation and 6 476,000,000 tons by the second. 



The Pittsburg coal, with an estimated thickness of four feet, has a computed 

 area of 1,250 square miles, and a tonnage of 5,600,000,000 tons. Finally, the Meigs 

 Creek coal shows a tonnage of 2,777,000,000 tons, on an area of 620 square miles and 

 with a thickness of four feet. 



The sum of these several results exceeds 40,000,000,000 tons by the first computa- 

 tion and 23,000,000,000 by the second. The total acreage of the measured seams of 

 the State is 8,893 square miles by the first measurement and 5,032 square miles by 

 the second, and the average thickness is estimated as four feet. 



But, even were these figures entirely within the mark, there would be large 

 abatements necessary in the computation of our coal resources. In all coal mining 

 a certain percentage of loss must be provided for. It never falls below ten per cent., 

 and it sometimes reaches fort}- per cent. I will estimate the loss in Ohio mining at 

 twenty per cent. 



Again, all of our seams have suffered more or less loss from erosion that took 

 place during or immediately succeeding their formation, and this may be styled 

 contemporaneous erosion. The losses in our best fields from this source are con- 

 siderable. I will put them at ten per cent. Finally, "wants" occur in every field, 

 and, including in this reduction the areas that have already been worked out, I should 

 be disposed to reduce the figures by at least twenty per cent. These three sources 

 of loss make a total abatement of fifty per cent., thus leaving an available supply of 



