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 undisturbed 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.