s of the United States had their
plants allied to the Lepidodendron. But the group in which these occur
has since been transferred from the Upper Silurian to the Old Red
System; and we find it expressly stated by Professor H. D. Rogers, in
his valuable contribution to the "Physical Atlas" (second edition,
1856), that "the Cadent [or Lower Old Red] strata are the oldest
American formations in which remains of a true terrestrial vegetation
have yet been discovered." It has been shown, too, by Sir Roderick
Murchison, that the supposed Silurian plants of Oporto are in reality
Carboniferous, and owe their apparent position to a reverse folding of
the strata. I have already referred to the solitary spore-cases of the
Ludlow Rocks; and beneath these rocks, says Sir Roderick (1854), "no
remains of plants have been discovered which are recognizably of
terrestrial origin." Scanty, too, as the terrestrial flora of the Old
Red Sandstone everywhere is, we find it exhibiting very definitely the
leading Palaeozoic features. Its prevailing plants are the ferns and
their apparent allies. It has in our own country, as has been just
shown, its ferns, its lepidodendra, its striated plants allied to the
calamites, and its decided araucanite; in America, in the Cadent series,
it had its "plants allied to ferns and lepidodendra;" and in the
Devonian basin of Sabero in Spain, its characteristic organisms are, a
lepidodendron (_L. Chemungensis_), and a very peculiar fern
(_Sphenopteris laxus_).[52] But while in its main features it resembled
the succeeding flora of the Carboniferous period, it seems in all its
forms to have been specifically distinct. It was the independent flora
of an earlier creation than that to which we owe the coal. For the
meagreness of the paper in which I have attempted to describe it as it
occurs in Scotland, I have but one apology to offer. My lecture contains
but little; but then, such is the scantiness of the materials on which I
had to work, that it could not have contained much: if, according to the
dramatist, the "amount be beggarly," it is because the "boxes are
empty." Partly, apparently, from the circumstance that the organisms of
this flora were ill suited for preservation in the rocks, and partly
because, judging from what appears, the most ancient lands of the globe
were widely scattered and of narrow extent, this oldest of the floras is
everywhere the most meagre.

LECTURE TWELFTH.

ON THE LESS KNO