forests: long withdrawing lakes, fringed with dense thickets of the green Calamite, tall and straight as the masts of pinnaces, and inhabited by enormous fishes, that glittered through the transparent depths in their enamelled armour of proof; or glades of thickest verdure, where the tree-fern mingled its branch-like fronds with the hirsute arms of the gigantic club-moss, and where, amid strange forms of shrub and tree no longer known on earth, the stately Araucarian reared its proud head two hundred feet over the soil; or yet again, there rose a scene of coral bowers and encrinal thickets, that glimmered amid the deep green of the ancient ocean, and in which, as in the groves sung by Ovid, the plants were sentient, and the shrinking flowers bled when injured. And, last of all, on the further limits of organic life a thick fog came down upon the sea, and my excursions into the remote past terminated, like the voyage of an old fabulous navigator, in thick darkness. Each of the series of visions, whether of the comparatively recent or the remote past, in which I at that time indulged, had employed the same faculties and gratified the same feelings; and though, in surveying the stuff out of which they had been sublimed, I could easily say where the historic ended and the geologic began, no corresponding line indicated in the visions themselves where the poetry ended and the prose began. The visions, whether historic or geologic, 'were of imagination all compact.' They all involved the same processes of mindthough, of course, in this instance, mind of a humbler order and ruder texture-as those exhibited in the sweet and fragrant verse of the poet himself,-as those exercised, let me say, in his vision on 'Mary's Mount,' when, with quiet graves above, and surrounded by quiet fields, he saw the contending hosts of a former day thronging the lower ground, and,

'With hilt to hilt, and hand to hand,

The children of our mother land
To battle came;'

or when he called up, after the lapse of half a lifetime, how when, in a wintry morning, he had journeyed before daybreak, a happy boy, along the frozen Esk, and saw

'In the far west the Pentland's gloomy ridge

Belting the pale blue sky, whereon a cloud,
Fantastic, grey, and tinged with solemn light,
Lay like a dreaming monster, and the moon,
Waning, above its silvery rim upheld

Her horns, as 'twere a spectre of the past.'

I shall continue to hold, therefore, that there was no real difference between the views of the poet and those which I myself entertain, but that, as he himself well expressed it, our 'apparent antagonism arose simply from the opposite aspects in which we had viewed the subject.' He had been thinking of but stiff diagrams and hard names,-of dead strata measured off, in 'geological exposition,' by the yard and the mile, and enveloped in the obscuring folds of a Babylonish phraseology: while I, looking through the crooked characters and uncouth sounds in which the meanings of the science are locked up, to the meanings themselves, was luxuriating among the strange wild narratives and richly poetic descriptions of which its pregnant records consist.

What is it, let me ask, that imparts to Nature its poetry? It is not in Nature itself; it resides not either in dead or organized matter,-in rock, or bird, or flower; 'the deep saith, It is not in me, and the sea saith, It is not in me.' It is in mind that it lives and breathes: external nature is but its storehouse of subjects and models; and it is not until these are called up as images, and invested with 'the light that never was on land or sea,' that they cease to be of the earth earthy, and form the ethereal stuff of which the visions of the poet are made. Nay, is it not mainly through that associative faculty to which the sights and sounds of present nature become suggestive of the images of a nature not present, but seen within the mind, that the landscape pleases,

or that we find beauty in its woods or beside its streams, or the impressive and the sublime among its mountains and rocks? Nature is a vast tablet, inscribed with signs, each of which has its own significancy, and becomes poetry in the mind when read; and geology is simply the key by which myriads of these signs, hitherto undecipherable, can be unlocked and perused, and thus a new province added to the poetical domain. We are told by travellers, that the rocks of the wilderness of Sinai are lettered over with strange characters, inscribed during the forty years' wanderings of Israel. They testify, in their very existence, of a remote past, when the cloud-o'ershadowed tabernacle rose amid the tents of the desert; and who shall dare say whether to the scholar who could dive into their hidden meanings they might not be found charged with the very songs sung of old by Moses and by Miriam, when the sea rolled over the pride of Egypt? To the geologist every rock bears its inscription engraved in ancient hieroglyphic characters, that tell of the Creator's journeyings of old, of the laws which He gave, the tabernacles which He reared, and the marvels which He wrought, -of mute prophecies wrapped up in type and symbol,—of earth gulfs that opened, and of reptiles that flew,-of fiery plagues that devastated on the dry land, and of hosts more numerous than that of Pharaoh, that 'sank like lead in the mighty waters; and, having in some degree mastered the occult meanings of these strange hieroglyphics, we must be permitted to refer, in asserting the poetry of our science, to the sublime revelations with which they are charged, and the vivid imagery which they conjure up. But our history lags in its progress, while we discuss the poetic capabilities of the study through which its records are read and its materials derived.

In the deposits of that Tertiary division of the geologic formation which represents in the history of the globe the period during which mammals began to be abundant, and in

which the great Cuvier won his laurels, Scotland is one of the poorest of European countries. Save for the comparatively recent discovery of Tertiary beds in the island of Mull by a nobleman fitted by nature either to adorn the literature or extend the science of his country, the geological historian would have to pass direct from the Pleistocene beds, with their grooved and polished pebbles and their semi-arctic shells, to the Chalk fossils of Banff and Aberdeen. But the discovery of his Grace the Duke of Argyll furnishes us with an interesting glimpse of a middle period widely different in its character from either the Cretaceous system or the boulder-clay. In the island of Mull, in a headland that rises about 130 feet over the sea, there occur, interposed between thick beds of trap, three comparatively thin beds of a grey arenaceous shale, charged with fossil leaves, as beautifully spread out, and with their ribs and veins as distinctly visible, as if they had been preserved in the herbarium of a botanist. Most of them belong to extinct species of existing families of dicotyledonous trees, such as the plane and the buckthorn, mingled, however, with narrow linear leaves of cone-bearing trees, which are supposed to belong, in this instance, to a species of yew, and with what seem the fronds of fern and the stems of equisetaceæ. Some of the beds of coal which have been long known to occur among the traps of the island of Mull are regarded by the Duke of Argyll as prolongations of these Tertiary leaf-beds, so mineralized by some metamorphic action as to have lost the organic structure. There must have been vast accumulations of leaves ere they could have yielded beds of coal. The middle or second bed of the three his Grace describes as peculiarly rich in the leafy impressions of this ancient period; and I need scarce say how suggestive the glimpse is which is furnished us by these buried layers of the foliage of Tertiary forests in Scotland, of which no other known memorial remains. You all remember Coleridge's fine comparison of the sorely-worn sails

of the vessel in which the ancient mariner performed his voyage of peril and prodigy, to

'Brown skeletons of leaves that lay

The forest brook along,

When the ivy tod is heavy with snow,

And the owlet whoops to the wolf below;'

and you must have often marked the extreme delicacy of those deposited leaves, macerated during the winter season at the bottom of some woodland pool, which suggested the poet's simile. In that Tertiary period to which the leafbeds of Mull belong, it would seem that extensive forests, chiefly of deciduous trees, shed year after year their summer coverings of leaves, some of which fell, and some of which were blown by the autumnal gusts, into the streams of the country, and were swept down by the current to lakes or estuaries, where they lay gradually resolving into such brown skeletons as caught the eye of Coleridge. We learn further, that there were forces active at the time, of which at any later period we have had no examples in the British islands. One of the leaf-beds described by his Grace is overlaid by a bed of volcanic ashes or tuff seven feet thick ; another by a bed of similar ashes mixed with chalk flints, twenty feet thick; and yet another-the topmost layerbears over it a bed of overflowing columnar basalt, forty feet thick. The volcanic agencies were active in what is now Scotland during the ages of its Tertiary forests.

The only Tertiary fossils of Scotland yet discovered are these forest and fern leaves of the Mull deposits. Their place in the great geologic division to which they belong is still definitely to fix; but some of our higher geologists are, I find, disposed to refer them to the second Tertiary or Miocene epoch, though with considerable hesitation. They belong, it is probable, to a period not very widely removed from that of the richly fossiliferous Marlstone of Eningen, on the banks of the Rhine, with its vast abundance of