isturbed by its operations? The thought has
often struck me that calcined lime, cast out as ashes from some distant
crater and carried by the winds, might have been the cause of the widely
spread destruction to which the fossil organisms testify. I have seen
the fish of a small trouting stream, over which a bridge was in the
course of building, destroyed in a single hour, for a full mile below
the erection, by a few troughfuls of lime that fell into the water when
the centring was removed.

The period of death passed, and over the innumerable dead there settled
a soft muddy sediment. For an unknown space of time, represented in the
formation by a deposit about fifty feet in thickness, the waters of the
depopulated area seem to have remained devoid of life. A few scales and
plates then begin to appear. The fish that had existed outside the chasm
seem to have gradually gained upon it as their numbers increased.

The work of deposition went on and sandstone was overlaid by stratified
clay. This upper bed had also its organisms, but the circumstances were
less favourable to the preservation of entire ichthyolites than those in
which the organisms were wrapped up in their stony coverings. Age
followed age, generations were entombed in ever-growing depositions.
Vast periods passed, and it seemed as if the power of the Creator had
reached its extreme limit when fishes had been called into existence,
and our planet was destined to be the dwelling-place of no nobler
inhabitants.

The curtain rises, and the scene is new. The myriads of the lower
formation have disappeared, and we are surrounded on an upper platform
by the existences of a later creation. Shoals of cephalaspides,
feathered with fins, sweep past. We see the distant gleam of scales,
that some of the coats glitter with enamel, that others bristle over
with minute thorny points. A huge crustacean, of uncouth proportions,
stalks over the weedy bottoms, or burrows in the hollows of the banks.
Ages and centuries pass--who can sum up their number?--for the depth of
this middle formation greatly exceeds that of the other two.

The curtain rises. A last day had at length come to the period of the
middle formation, and in an ocean roughened by waves and agitated by
currents we find new races of existences. We may mark the clumsy bulk of
the Holoptychius conspicuous in the group. The shark family have their
representative as before; a new variety of the pterichthys spreads