One portion, B-C, of this seam of coal is now inclined; the area of the
swamp having subsided as much as 25 feet at E-C, and become for a time submerged
under salt, fresh, or brackish water. Some of the trees of the original forest
A-B-C fell down, others continued to stand erect in the new lagoon, their stumps
and part of their trunks becoming gradually enveloped in layers of sand and mud,
which at length filled up the new piece of water C-E.
When this lagoon has been entirely silted up and converted into land, the
forest-covered surface A-B will extend once more over the whole area A-B-E, and
a second mass of vegetable matter, D-E, forming three feet more of coal, will
accumulate. We then find in the region E-C two seams of coals, each three feet
thick, with their respective under-clays, with erect buried trees based upon the
surface of the lower coal, the two seams being separated by 25 feet of
intervening shale and sandstone. Whereas in the region A-B, where the growth of
the forest has never been interrupted by submergence, there will simply be one
seam, two yards thick, corresponding to the united thickness of the beds B-E and
B-C.
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