persistency, united to a great extent, in the various platforms of the Coal Measures, and of ever-recurring subsidence and depression, which accumulated one surface platform over another for hundreds and thousands of feet, belongs, I am compelled to hold, to a condition of things no longer witnessed on the face of the globe. The earth has still its morasses, its deltas, its dismal swamps; it has still, too, its sudden subsidences of surface, by which tracts of forest have been laid under water; but morasses and deltas cover only very limited tracts, and sudden subsidences are at once very exceptional and merely local occurrences. Subsidence during the Carboniferous ages, though interrupted by occasional periods of rest, and occasional paroxysms of upheaval, seems, on the contrary, to have been one of the fixed and calculable processes of nature; and, from apparently the same cause, persistent swamps, and accumulations of vegetable matter, that equalled continents in their extent, formed one of the common and ordinary features of the time.

My subject is one on which great diversity of opinion may and does prevail. But, while entertaining a thorough respect for the judgment and the high scientific acquirements of geologists who hold that the earth existed at this early period in the same physical conditions as it does. now, I must persist in believing that these conditions were in one important respect essentially different; I must persist in believing that our planet was greatly more plastic and yielding than in these later times; and that the molten abyss from which all the Plutonic rocks were derived, - that abyss to whose existence the earthquakes of the historic period and the recent volcanoes so significantly testify, was enveloped by a crust comparatively thin. Like the thin ice of the earlier winter frosts, that yields

under the too adventurous skater, it could not support

great weights, table-lands such as now exist, or mountain chains; and hence, apparently, the existence of vast swampy plains nearly level with the sea, and ever-recurring periods of subsidence, wherever a course of deposition had overloaded the surface. The yet further fact, that as we ascend into the middle and earlier Palæozoic periods, the traces of land become less and less frequent, until at length scarce a vestige of a terrestrial plant or animal occurs in entire formations, seems charged with a corroborative evidence. I shall not say that in these primeval periods

"A shoreless ocean tumbled round the globe,"

for the terrestrial plants of the Silurians show that land existed in even the earliest ages in which, so far as the geologist knows, vitality was associated with matter; but it would seem that only a few insulated parts of the earth's surface had got their heads above water at the time. The thin and partially consolidated crust could not bear the load of great continents; nor were the “mountains yet settled, nor the hills brought forth.” It would seem that not until the Carboniferous ages did there exist a period in which the slowly-ripening planet could exhibit any very considerable breadth of land; and even then it seems to have been a land consisting of immense flats, unvaried, mayhap, by a single hill, in which dreary swamps, inhabited by doleful creatures, spread out on every hand for hundreds and thousands of miles, and a gigantic and monstrous vegetation formed, as I have shown, the only prominent feature of the scenery. Burnett held that the earth, previous to the Flood, was one vast plain, without hill or valley, and that Paradise itself, like the blomen

garten of a wealthy Dutch burgomaster, was curiously laid out upon a flat. We would all greatly prefer the Paradise of Milton:

"A happy rural seat of various views,

Where lawns and level downs, whitened with flocks
Grazing the tender herb, were interposed

With palmy hillocks and irrageous vales

Luxuriant; and where murmuring waters fell

Down the steep hills dispersed, or in blue lakes
Embraced the fringed banks, with myrtle crowned."

It was during the times of the Coal Measures that Burnett would have found his idea of a perfect earth most nearly realized, in at least general outline; but even he would scarce have deemed it a paradise. Its lands were lands in which, according to the Prophet, there "could no man have dwelt, nor son of man passed through." From some tall tree-top the eye would have wandered, without resting-place, over a wilderness of rank, unwholesome morass, dank with a sombre vegetation, that stretched on and away from the foreground to the distant horizon, and for hundreds and hundreds of leagues beyond; the woods themselves, tangled, and dank, and brown, would, according to the poet, have "breathed a creeping horror o'er the frame;" the surface, even where most consolidated, would have exhibited its frequent ague-fits and earth-waves; and, after some mightier earthquake had billowed the landscape, dashing together the crests of tall trees and gigantic shrubs, there would be a roar, as of many waters, heard from the distant outskirts of the scene, and one long wall of breakers seen stretching along the line where earth and sky meet, stretching inwards, and travelling onwards with yet louder and louder roar, - Calamite and Ulodendron, Sigillaria and Tree-fern, disappearing amid the foam,

until at length all would be submerged, and only here and there a few Araucarian tops seen over a sea without visible shore. Such was the character, and such were the revolutions, of the land of the Carboniferous era, a land that seems to have been called into being less for the sake of its own existence than for that of the existences of the future.

LECTURE SIXTH.

Remote Antiquity of the Old Red Sandstone-Suggestive of the vast Tracts of Time with which the Geologist has to deal - Its great Depth and Extent in Scotland and England - Peculiarity of its Scenery - Reflection on first discovering the Outline of a Fragment of the Asterolepis traced on one of its Rocks-Consists of Three Distinct Formations Their Vegetable Organisms -The Caithness Flagstones, how formed - The Fauna of the Old Red Sandstone-The Pterichthys of the Upper or Newest Formation - The Cephalaspis of the Lower Formation - The Middle Formation the most abundant in Organic Remains-Destruction of Animal Life in the Formation sudden and violent - The Asterolepis and Coccosteus - The Silurian the Oldest of the Geologic Systems - That in which Animal and Vegetable Life had their earliest beginnings-The Theologians and Geologists on the Antiquity of the GlobeExtent of the Silurian System in Scotland-The Classic Scenery of the Country situated on it - Comparatively Poor in Animal and Vegetable Organisms The Unfossiliferous Primary Rocks of Scotland -Its Highland Scenery formed of them - Description of Glencoe Other Highland Scenery glanced atProbable Depth of the Primary Stratified Rocks of Scotland - How deposited -Speculations of Philosophers regarding the Processes to which the Earth owes its present Form - The Author's Views on the subject.

I INCIDENTALLY mentioned, when describing the Oolitic productions of our country, that the shrubs and trees of this Secondary period grew, on what is now the east coast of Sutherland, in a soil which rested over rocks of Old Red Sandstone, and was composed mainly, like that of the county of Caithness in the present day, of the broken debris of this ancient system. We detect fragments of the Old Red flagstones still fast jammed among the petrified roots of old Oolitic trees; we find their water-rolled pebbles existing as a breccia, mixed up with the bones of huge Oolitic reptiles and the shells of extinct Oolitic molluscs;