It may be affirmed that generally, in the "cypress swamps" of the Mississippi,
no sediment mingles with the vegetable matter accumulated there from the decay
of trees and semi-aquatic plants. As a singular proof of this fact, I may
mention that whenever any part of a swamp in Louisiana is dried up, during an
unusually hot season, and the wood set on fire, pits are burnt into the ground
many feet deep, or as far down as the fire can descend without meeting with
water, and it is then found that scarcely any residuum or earthy matter is left.
At the bottom of all these "cypress swamps" a bed of clay is found, with roots
of the tall cypress (Taxodium distichum), just as the under-clays of the coal
are filled with Stigmaria.
CONVERSION OF COAL INTO ANTHRACITE.
It appears from the researches of Liebig and other eminent chemists, that when
wood and vegetable matter are buried in the earth exposed to moisture, and
partially or entirely excluded from the air, they decompose slowly and evolve
carbonic acid gas, thus parting with a portion of their original oxygen. By this
means they become gradually converted into lignite or wood-coal, which contains
a larger proportion of hydrogen than wood does.
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