whole forest of such trees shedding in due season their copious showers
of spores to earth, we shall perhaps be less amazed than we were at first
thought, at the stupendous result wrought out by so minute an object.

Another well-known form of carboniferous vegetation is that known as the
_Sigillaria_, and, connected with this form is one, which was long
familiar under the name of _Stigmaria_, but which has since been
satisfactorily proved to have formed the branching root of the
sigillaria. The older geologists were in the habit of placing these
plants among the tree-ferns, principally on account of the cicatrices
which were left at the junctions of the leaf-stalks with the stem, after
the former had fallen off. No foliage had, however, been met with which
was actually attached to the plants, and hence, when it was discovered
that some of them had long attenuated leaves not at all like those
possessed by ferns, geologists were compelled to abandon this
classification of them, and even now no satisfactory reference to
existing orders of them has been made, owing to their anomalous
structure. The stems are fluted from base to stem, although this is not
so apparent near the base, whilst the raised prominences which now form
the cicatrices, are arranged at regular distances within the vertical
grooves.

When they have remained standing for some length of time, and the strata
have been allowed quietly to accumulate around the trunks, they have
escaped compression. They were evidently, to a great extent, hollow like
a reed, so that in those trees which still remain vertical, the interior
has become filled up by a coat of sandstone, whilst the bark has become
transformed into an envelope of an inch, or half an inch of coal. But
many are found lying in the strata in a horizontal plane. These have been
cast down and covered up by an ever-increasing load of strata, so that