h rested over it
were composed, in the descending order, first, of a conglomerate thirty
feet thick; secondly, of a red rock four feet thick; thirdly, of
twenty-eight feet of the soft shaly substance known to the quarriers as
caulm; and fourthly, of more than nine feet of gray pavement,
immediately under which, in a soft, argillaceous stratum, lay the
organism. It was about four feet in length, bulged out at the lower end
into a bulb-like protuberance, which may have been, however, merely an
accidental result of its state of keeping; and threw off, at an acute
angle, two branches about a foot from the top. It was covered with a
bark of brittle coal, which is, however, wanting in all the fragments
that have been preserved; and was resolved internally into a brown
calcareous substance of about the hardness of ordinary marble, and very
much resembling that into which the petrifactive agencies have
consolidated the fossil trees of Granton and Craigleith. From the
decorticated condition of the surviving fragments, and the imperfect
preservation of the interior structure, in all save the central portions
of its transverse sections, it yields no specific marks by which to
distinguish it; but enough remains in its irregular network of cells,
devoid of linear arrangement, and untraversed by medullary rays, to
demonstrate its generic standing as a Lepidodendron.

[It has been questioned whether the lower place in the Old Red System
should be assigned to the flagstones of Caithness and Ross, with their
characteristic Dipterus and Coccosteus beds, or to the gray tilestones
of Forfar and Kincardineshires, with their equally characteristic
Cephalaspis. The evidence on the point is certainly not so conclusive as
I deemed it fifteen years ago, when our highest authority on the subject
not only regarded the tilestone of the Silurian regions of England as a
member of the Old Red Sandstone (an arrangement which I am still
disposed to deem the true one), but also held further, that there had
been detected in this formation near Downtown Castle, Herefordshire,
broken remains of _Dipterus macrolepidotus_, one of the best marked
ichthyolites of the flagstones of Caithness and Orkney. A great and
unbroken series of fossiliferous rocks, with Dipterus at its base,
Cephalaspis in its medial spaces, and Holoptychius at its top, might
well be regarded as the analogue of the Old Red of Scotland, with the
Caithness flagstones ranged at its bottom, th