376 GEOLOGICAL SURVEY OF THE TERRITORIES. 



is essentially of two kinds. Either the vegetables which furnish the 

 materials are aquatic, or semi-aerial plants, having their roots in water, 

 and expanding their branches, leaves, &c, on the surface of the water, 

 or above it. Their debris falls in water, and are heaped and preserved 

 under it. In another way, and this is more generally the case, the 

 plants of the peat bogs are of a peculiar texture. Hygrometrical, like 

 sponges, they absorb humidity by their aerial tissues as much as by 

 their roots, and thus protected themselves against decomposition from 

 atmospheric action, they cover in their growth every kind of woody 

 debris, even large trees, and afford to them the same protective in- 

 fluence. In that way the surface of peat-bogs of this kind grow 

 constantly up. In that way also peat-bogs grow at our time upon 

 the slopes of steep mountains, whenever atmospheric humidity is con- 

 stant and abundant enough to furnish moisture for the life of those 

 hygrometrical plants, which now are mere mosses. The peat-bogs of the 

 coal did grow in the same way; the distinction in cannel coal, which 

 has been formed under water, and bituminous coal, which by its layers 

 indicates an upper aquatic growth, is well marked. But during the 

 carboniferous epoch, the circumstances favorable to the growth of the 

 peat were in their highest development. Low, wide basins of stagnant 

 water, whose bottom was first coated by deposits of clay ; an atmosphere 

 constantly charged with vapors and a large proportion of carbonic 

 acid, the food of plants, forming by its transformation the woody 

 tissues ; floating vegetables of immense size, first growing horizon- 

 tally at the surface of the water, and filling the basin with their 

 debris, then forming a support for a more aerial vegetation ; fern- 

 trees, lycopodes, horse-tails, all of enormous size, heaped in a con- 

 tinuous growth the woody tissues of their vegetable remains in a 

 now inconceivable proportion. Our thickest beds of peat now 

 measure scarcely twenty feet. By compression and mineralization the 

 thickness would be reduced to one-sixth, or three feet at the most. We 

 have beds of coal of twenty feet of thickness which would make a de- 

 posit of peat reach one hundred and twenty feet. And now the result 

 of this wonderful accumulation of fossilized debris of plants of the car- 

 boniferous epoch is known to everybody. We will not repeat what 

 Taylor, Bogers, Lesley, Sheaffer, and others have published on the extent 

 of our coal-measures and on their coal-bearing capacity. The area cov- 

 ered by the carboniferous formations in the United States comprises 

 about one hundred and forty thousand square miles. It is true, indeed, 

 that the peat bogs of old did not extend over the whole surface ; that 

 they were of various dimensions, separated by sandy hills or by deep 

 lagoons; that after the deposit of their materials, erosions caused by 

 water or other agency have greatly diminished their size. But it is true 

 also that beds of coal, like the Pittsburg bed, whose average thickness 

 is about eight feet, may be traced over surfaces more than one hundred 

 square miles in width. It is equally true that beds of coal are superposed 

 at intervals, in the coal measures, in such a way that at the same place a 

 boring of a few hundred feet may successively pass through five beds of 

 coal or even more of various thicknesses. A boring of seven hundred and 

 fifty feet, recently made in the anthracite coal basin of Pennsylvania, 

 passed through five beds of coal, respectively, four, eleven, five, twenty- 

 eight, and five feet thick, or more than fifty feet of anthracite, with 

 intervals of rocks, respectively two hundred and sixty, ninety-eight, 

 one hundred and seventy-four, and one hundred and thirty-six feet. 

 A section at Wilkesbarre, Pennsylvania, indicates sixty-two feet of coal 

 in a thickness of about six hundred feet of measures. A low bed of 



