The absence of sulphurets,
and the occurrence of carbonate of iron in connection with
them, prove that, when they existed as soils, rain-water, and
not sea-water, percolated them. (5) The coal and the fossil
forests present many evidences of subaerial conditions. Most
of the erect and prostrate trees had become hollow shells of
bark before they were finally embedded, and their wood had
broken into cubical pieces of mineral charcoal. Land-snails
and galley-worms _Xylobius_ crept into them, and they became
dens, or traps, for reptiles. Large quantities of mineral
charcoal occur on the surface of all the large beds of
coal. None of these appearances could have been produced by
subaqueous action. (6) Though the roots of the _Sigillaria_
bear more resemblance to the rhizomes of certain aquatic
plants; yet, structurally, they are absolutely identical with
the roots of Cycads, which the stems also resemble. Further,
the _Sigillariae_ grew on the same soils which supported
Conifers, _Lepidodendra, Cordaites_, and Ferns--plants which
could not have grown in water. Again, with the exception
perhaps of some _Pinnulariae_ and _Asterophyllites_, there
is a remarkable absence from the coal measures of any form of
properly aquatic vegetation.
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