500 



UXIOX OF COAL SEAMS. 



[Ch. XXV. 



sively uuite ; so that at last they form one mass, between 40 and 50 

 feet thick. I saw this enormons bed of anthracitic coal quarried in 

 the open air at Mauch Chunk (or the Bear Mountain), the overlying 

 sandstone, 40 feet thick, having been removed bodily from the top of 

 the hill, which, to use the miner's expression, had been " scalped." 

 The accumulation of vegetable matter now constituting this vast bed 

 of anthracite, may perhaps, before it was condensed by pressure and 

 the discharge of its hydrogen, oxygen, and other volatile ingredients, 

 have been between 200 and 300 feet thick. The origin of such a vast 

 thickness of vegetable remains, so unmixed with earthy ingredients, 

 can, I think, be accounted for in no other way, than by the growth, 

 during thousands of years, of trees and ferns, in the manner of peat, — 

 a theory which the presence of the Stigmaria in situ under each of the 

 seven layers of anthracite, fully bears out. The rival hypothesis, of 

 the drifting of plants into a sea or estuary, leaves the absence of 

 sediment, or, in this case, of clay, sand, and pebbles, wholly unex- 

 plained. 



But the student will naturally ask, what can have caused so many 

 seams of coal, after they had been persistent for miles, to come to- 

 gether and blend into one single seam, and that one equal in the 

 aggregate to the thickness of the several separate seams ? Often had 

 the same question been put by English miners before a satisfactory 

 answer was given to it by the late Mr. Bowman. The following is his 

 solution of the problem : Let a a', fig. 553, be a mass of vegetable 



Fig. 553. 



matter, capable, when condensed, of forming a 3-foot seam of coal. It 

 rests on the underclay b b', filled with roots of trees in situ, and it 

 supports a growing forest (c d). Suppose that part of the same forest 

 d e had become submerged by the ground sinking down 25 feet, so 

 that the trees have been partly thrown down and partly remain erect 

 in water, slowly decaying, their stumps and the lower parts of their 

 trunks being enveloped in layers of sand and mud, which are gradually 

 filling up the lake d f. When this lake or lagoon has at length been 

 entirely silted up and converted into land, say, in the course of a 

 century, the forest c d will extend once more continuously over the 

 whole area c f, as in fig. 554, and another mass of vegetable matter 



