No. 136.J 73 



the coal layers are inters tratified. These strata* of coal are of 

 all thicknesses, from a few inches up to twenty or even forty 

 feet, and are separated from each other by masses of rock of 

 from ten or twenty to two or three hundred feet thick, and they 

 are mined in various ways according to their situation : in a few 

 places, where they are covered by but little rock, being quarried 

 in open daylight ; in others, mined by galleries or tunnels driven 

 into the hillsides on a level ; in others, by deep pits. 



Geological investigation in all coal countries has led to the 

 conclusion that these strata of coal are vegetable matter, which 

 during the Carboniferous epoch appears to have reached an enor- 

 mous and luxuriant growth, and formed vast accumulations, 

 which, after being buried under the marine sediments of sand 

 and clay which now form the slates and sandstones over them, 

 underwent the chemical changes which transformed them to their 

 present condition.* The proofs of this are found in the facts 

 that the rocks above and below the coal seams are filled with 

 vegetable remains, leaves, stems, roots, etc. ; the trunks of the 

 trees being in some places found still erect and standing upon 

 their roots, but converted into coal ; and that even the coal itself, 

 though in most cases it is solidified into one mass so as to show 

 no organic structure, displays in other instances, under the 

 microscope, all the texture of wood, the cells, the ducts through 

 which the sap once circulated, and even minute markings by 

 which it can be determined whether the wood belonged to one or 

 another general class of trees ; for instance, whether it was a 

 cone-bearing tree like the pine, or one of another family. 



This vegetable origin of all the coal seems well-established ; 

 but the mode in which such great accumulations of it were made 

 over such vast areas,* is yet an obscure question. The prevail- 

 ing opinion is that it grew in enormous morasses or swampy 

 tracts, resembling on a larger scale the Great Dismal swamp, or 

 the Okefenoke swamp of Georgia ; in which the annual fall of 

 leaves, branches, and trunks at last formed thick peaty masses, 

 which, being submerged under the sea and covered with sedi- 

 ments, became the vast piles of fossil fuel which are now of so 

 great importance to our race. 



* A single bed of coal, that called the Pittsburgh seam, is known to extend over no lesg 

 than 14000 square miles, with a usual thickness of from four to ten feet. Other layers^ 

 though less in extent, are much greater iu thickness, reaching even forty feet. 



[Assembly, No. 136.] 10 



