hand, that the
crustaceans of the gray tilestones of Forfar and Kincardine not a little
resemble those of the Upper Silurian and red tilestone beds of England;
and that, judging from the ichthyodorulites found in both, their fishes
must have been at least generically allied. The crustaceans of the upper
Silurian of Lesmahagow, too, seem certainly much akin to those of the
Forfarshire tilestones.]

[Illustration: Fig. 124.

CYCLOPTERUS HIBERNICUS.]

Above this gray tilestone formation lies the Upper Old Red Sandstone,
with its peculiar group of ichthyic organisms, none of which seem
specially identical with those of either the Caithness or the
Forfarshire beds. For it is an interesting circumstance, suggestive
surely of the vast periods which must have elapsed during its
deposition, that the great Old Red System has, as I have just said, its
three distinct platforms of organic existence, each wholly different
from the others. Generically and in the group, however, the Upper fishes
much more closely resemble, I repeat, the fishes of the Lower or
Caithness and Cromarty platform, than they do those of the Forfarshire
and Kincardine one. The vegetable remains of the Upper formation in
Scotland are both rare and ill preserved. I have seen what I deemed
fucoidal markings dimly impressed on the planes of some of the strata,
not in the carbonaceous form so common in the other two formations, but
as mere colored films of a deeper red than the surrounding matrix.
Further, I have detected in the same beds, and existing in the same
state, fragments of a striated organism, which may have formed part of
either a true calamite, like those of the Coal Measures, or of some such
striated but jointless vegetable as that of the Lower Old Red of Thurso
and Lerwick.[51] With these markings ferns are occasionally found; and
to one of these, from the light which it throws on the true place in the
scale of a series of deposits in a sister country, there attaches no
little interest. I owe my specimen to Mr. John Stewart of Edinburgh, who
laid it open in a micaceous red sandstone in the quarry of Prestonhaugh,
near Dunse, where it is associated with some of the better known
ichthyic organisms of the Upper Old Red Sandstone, such as _Pterichthys
major_ and _Holoptychius Nobilissimus_. Existing as but a deep red film
in the rock, with a tolerably well defined outline, but without trace of
the characteristic venation on which the fossil botanist,