l intelligent members of his session, to
whose kindness I owed, on the following day, introductions to some of
the less accessible curiosities of the place. I rose betimes on the
morning of Monday, that I might have leisure enough before me to see
them all, and broke my first ground in Orkney as a geologist in a quarry
a few hundred yards to the south and east of the town. It is strange
enough how frequently the explorer in the Old Red finds himself
restricted in a locality to well nigh a single organism,--an effect,
probably, of some gregarious instinct in the ancient fishes of this
formation, similar to that which characterizes so many of the fishes of
the present time, or of some peculiarity in their constitution, which
made each choose for itself a peculiar habitat. In this quarry, though
abounding in broken remains, I found scarce a single fragment which did
not belong to an exceedingly minute species of Coccosteus, of which my
first specimen had been sent me a few years before by Mr. Robert Dick,
from the neighborhood of Thurso, and which I at that time, judging from
its general proportions, had set down as the young of the _Coccosteus
cuspidatus_. Its apparent gregariousness, too, quite as marked at Thurso
as in this quarry, had assisted, on the strength of an obvious enough
analogy, in leading to the conclusion. There are several species of the
existing fish, well known on our coasts, that, though solitary when
fully grown, are gregarious when young. The coal-fish, which as the
sillock of a few inches in length congregates by thousands, but as the
colum-saw of from two and a half to three feet is a solitary fish, forms
a familiar instance; and I had inferred that the Coccosteus, found
solitary, in most instances, when at its full size, had, like the
coal-fish, congregated in shoals when in a state of immaturity. But a
more careful examination of the specimens leads me to conclude that this
minute gregarious Coccosteus, so abundant in this locality that its
fragments thickly speckle the strata for hundreds of yards together--(in
one instance I found the dorsal plates of four individuals crowded into
a piece of flag barely six inches square)--was in reality a distinct
species. Though not more than one-fourth the size, measured linearly, of
the _Coccosteus decipiens_, its plates exhibit as many of those lines
of increment which gave to the occipital buckler of the creature its
tortoise-like appearance, and through wh