oration
and discovery still remains for us to do. We stand on the further edge
of the great floras of by-past creations, and have gathered but a few
handfuls of faded leaves, a few broken branches, a few decayed cones.

The Silurian deposits of our country have not yet furnished us with any
unequivocal traces of a terrestrial vegetation. Professor Nicol of
Aberdeen, on subjecting to the microscope the ashes of a Silurian
anthracite which occurs in Peeblesshire, detected in it minute tubular
fibres, which seem, he says, to indicate a higher class of vegetation
than the algae; but these may have belonged to a marine vegetation
notwithstanding. I detected some years ago, in the Trilobite-bearing
schists of Girvan, associated with graptolites of the Lower Silurian
type, a vegetable organism somewhat resembling the leaf of one of the
pond weeds,--an order of plants, some of whose species, such as Zostera,
find their proper habitats in salt water. I have placed beside this
specimen a fragment of the same graptolite-bearing rock, across which I
have pasted part of a leaf of _Zostera marina_, the only plant of our
Scottish seas which is furnished with true roots, bears real flowers
inclosed in herbaceous spathes, and produces a well formed farinaceous
seed. It will be seen, that in the few points of comparison which can be
instituted between forms so exceedingly simple, the ancient very closely
resembles the recent organism. It is not impossible, therefore, that
the Silurian vegetable may have belonged to some tribe of plants allied
to Zostera; and if so, we can easily conceive how the Silurian
anthracite of our country may be altogether of marine origin, and may
yet exhibit in its microscopic tubular fibres vestiges of a vegetation
higher than the algae.

[Illustration: Fig. 117.

_a_, SILURIAN ORGANISM. _b_, GRAPTOLITE. _c_, PORTION OF THE LEAF OF
ZOSTERA MARINA.]

[It were well, in dealing with the very ancient floras, in which
equivocal forms occur that might have belonged to either the land or the
sea, to keep in view those curious plants of the present time, the
habitats of which are decidedly marine, but which are marked by many of
the peculiarities of the seed-bearing plants of the land. The
superiority of Zostera to the common sea weeds of our coasts appears to
have struck in the north of Scotland eyes very little practised in such
matters, and seems to have given rise, in consequence, to a popular
myth. _Zoster