riod of the Upper Silurian
fish, properly so called, and of a very perfect organisation, had taken
precedence of the crustacean. These most ancient beings of their class
were cartilaginous fishes, and they appear to have been introduced by
myriads. Such are the remains of what seem to have been the first
vertebrata.

The history of the period represented by the Old Red Sandstone seems, in
what now forms the northern half of Scotland, to have opened amid
confusion and turmoil. The finely laminated Tilestones of England were
deposited evidently in a calm sea. During the contemporary period the
space which now includes Orkney, Lochness, Dingwall, Gamrie, and many a
thousand square miles besides, was the scene of a shallow ocean,
perplexed by powerful currents and agitated by waves. A vast stratum of
water-rolled pebbles, varying in depth from a hundred feet to a hundred
yards, remains, in a thousand different localities, to testify to the
disturbing agencies of this time of commotion, though it is difficult to
conceive how the bottom of any sea could have been so violently and
equally agitated for so greatly extended a space.

The period of this shallow and stormy ocean passed, and the bottom,
composed of the identical conglomerate which now forms the summit of
some of our loftiest mountains, sank to a depth so profound as to be
little affected by tides and tempests. During this second period there
took place a vast deposit of coarse sandstone strata, and the subsidence
continued until fully ninety feet had overlaid the conglomerate in
waters perfectly undisturbed. And here we find the first proof that this
ancient ocean literally swarmed with life--that its bottom was covered
with miniature forests of algae, and its waters darkened by immense
shoals of fish. I have seen the ichthyolite bed where they were as
thickly covered with fossil remains as I have ever seen a fishing-bank
covered with herrings.

At this period some terrible catastrophe involved in sudden destruction
the fish of an area at least a hundred miles from boundary to boundary,
perhaps much more. The same platform in Orkney as in Cromarty is strewn
thick with remains which exhibit unequivocally the marks of violent
death. In what could it have originated? By what quiet but potent agency
of destruction could the innumerable existences of an area perhaps ten
thousand miles in extent be annihilated at once, and yet the medium in
which they lived be left und