Ch. XXV.] 



UJSTION" OF COAL-SEAMS. 



391 



with beds of white grit and conglomerate of coarser grain than I ever 

 saw elsewhere, associated with pure .coal. The pebbles of quartz ar« 

 often of the size of a hen's egg. On following these pudding-stones and 

 grits for several miles from Pottsville, by Tamaqua, to the Lehigh Sum- 

 mit Mine, in company with Mr. H. D. Rogers, in 1841, he pointed out 

 to me that the coarse-grained strata and their accompanying shales 

 gradually thin out, until seven seams of coal, at first widely separated, 

 are brought nearer and nearer together, until they successively unite ; so 

 that at last they form one mass, between 40 and 50 feet thick. I saw 

 this enormous bed of anthracite coal quarried in the open air at Mauch 

 Chunk (or the Bear Mountain), the overlying sandstone, 40 feet ;.hick, 

 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 un- 

 mixed 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 sand and pebbles, wholly un- 

 explained. 



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

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

 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. 506, be a mass of vegetable matter, capable, 



Fig. 506. 



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 grow- 

 ing 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 de- 



