Ch. XXV.] HORIZONTAL COAL STRATA. 501 



(g g'), forming 3 feet more of coal, may accumulate from c to f. We 

 then find in the region f, two seams of coal (a! and g') each 3 feet 

 thick, and separated by 25 feet of sandstone and shale, with erect trees 

 based upon the lower coal, while, between d and c, we find these two 

 seams united in a 2-yard coal. It may be objected that the uninter- 

 rupted growth of plants during the interval of a century will have 

 caused the vegetable matter in the region c d to be thicker than the two 

 distinct scams a' and g' at f ; and no doubt there would actually be a 

 slight excess representing one generation of trees with the remains of 

 other plants, forming half an inch or an inch of coal ; but this would 

 not prevent the miner from affirming that the seam a g, throughout 

 the area c d, was equal to the two seams a' and g' at f. 



The reader has seen, by reference to the section (fig. 552 p. 497), 

 that the strata of the Appalachian coal-field assume an horizontal posi- 

 tion west of the mountains. In that less elevated country, the coal- 

 measures are . intersected by three great navigable rivers, and are 

 capable of furnishing for ages, to the inhabitants of a densely peopled 

 region, an inexhaustible supply of fuel. These rivers are the Monon- 

 gahela, the Alleghany, and the Ohio, all of which lay open on their 

 banks the level seams of coal. Looking down the first of these at 

 Brownsville, we have a fine view of the main seam of bituminous coal 

 10 feet thick, commonly called the Pittsburg seam, breaking out in 

 the steep cliff at the water's edge; and I made the accompanying 

 sketch of its appearance from the bridge over the river (see fig. 555). 

 Here the coal, 10 feet thick, is covered by carbonaceous shale (6), and 

 this again by micaceous sandstone (c). Horizontal galleries may be 

 driven everywhere at very slight expense, and so worked as to drain 

 themselves, while the cars, laden with coal and attached to each other, 

 glide down on a railway, so as to deliver their burden into barges 

 moored to the river's bank. The same seam is seen at a distance, on 

 the right bank (at a), and may be followed the whole way to Pitts- 

 burg, fifty miles distant. As it is nearly horizontal, while the river 

 descends it crops out at a continually increasing, but never at an in- 

 convenient, height above the Monongahela. Below the great bed of 

 coal at Brownsville is a fire-clay 1 8 inches thick, and below this, sev- 

 eral beds of limestone, below which again are other coal seams. I 

 have also shown in my sketch another layer of workable coal (at d d), 

 which breaks out on the slope of the hills at a greater height. Here 

 almost every proprietor can open a coal-pit on his own land, and the 

 stratification being very regular, he may calculate with precision the 

 depth at which coal may be won. 



The Appalachian coal-field, of which these strata form a part (from 

 c to e, section, fig. 552, p. 497), is remarkable for its vast area; for, 

 according to Professor H. D. Rogers, it stretches continuously from 

 N.E. to S.W., for a distance of 720 miles, its greatest width being 

 about 180 miles. On a moderate estimate, its superficial area amounts 

 to 63,000 square miles. 



