In the Oolite of Scotland I have, however, at length found trace of a vegetable organism that seems to have lain, if I may so express myself, outside the pentagon, and was not a member of any of the great families which it comprised. (See [Fig. 151.]) I succeeded about four years ago in disinterring from the limestone of Helmsdale what appears to be a true dicotyledonous leaf, with the fragment of another leaf, which I at first supposed might have belonged to a plant of the same great class, but which I now find might have been a portion of a fern. When Phlebopteris Phillipsii was first detected in the Oolite of Yorkshire, Lindley and Hatton, regarding it as dicotyledonous, originated their term Dictyophillum as a general one for all such leaves. But it has since been assigned to a greatly lower order,—the ferns; and Sir Charles Lyell has kindly shown me that an exotic fern of the present day exhibits exactly such a reticulated style of venation as my Helmsdale fragment. (See [Fig. 152], p. 497.) The other leaf, however, though also fragmentary, and but indifferently preserved, seems to be decidedly marked by the dicotyledonous character; and so I continue to regard it, provisionally at least, as one of the first precursors in Scotland of our great forest trees, and of so many of our flowering and fruit-bearing plants, and as apparently occupying the same relative place in advance of its contemporaries as that occupied by the conifer of the Old Red Sandstone in advance of the ferns and Lycopodaceæ with which I found it associated. In the arrangement of its larger veins the better preserved Oolitic leaf somewhat resembles that of the buckthorn; but its state of keeping is such that it has failed to leave its exterior outline in the stone.
One or two general remarks, in conclusion, on the Oolite flora of Scotland may be permitted me by the Association. In its aspect as a whole it greatly resembles the Oolite flora of Virginia, though separated in space from the locality in which the latter occurs by a distance of nearly four thousand miles. There are several species of plants common to both, such as Equisetum columnare, Calamites arenaceus, Pecopteris Whitbiensis, Lycopodites uncifolius, and apparently Tæniopteris magnifolia; both, too, manifest the great abundance in which they were developed of old by the beds of coal into which their remains have been converted. The coal of the Virginia Oolite has been profitably wrought for many years: it is stated by Sir Charles Lyell, who carefully examined the deposit, and has given as the results of his observation in his second series of Travels in the United States, that the annual quantity taken from the Oolitic pits by Philadelphia alone amounted to ten thousand tons; and though, on the other hand, the Sutherlandshire deposit has never been profitably wrought, it has been at least wrought more extensively than any other in the British Oolite. The seam of Brora, varying from three feet three to three feet eight inches in thickness, furnished, says Sir Roderick Murchison, between the years 1814 and 1826, no less than seventy thousand tons of coal. Such is its extent, too, that nearly thirty miles from the pit's mouth (in Ross-shire under the Northern Sutor) I have found it still existing, though in diminished proportions, as a decided coal seam, which it must have taken no small amount of vegetable matter to form. And almost on the other side of the world, nearly five thousand miles from the Sutherland beds, and more than eight thousand miles from the Carolina ones, the same Oolitic flora again appears, associated with beds of coal. At Nagpur in Central India the Oolitic Sandstones abound in simple fronded ferns, such us Tæniopteris and Glossopteris, and has its Zamites, its coniferous leaves, and its equisetaceæ.
Compared with existing floras, that of our Scottish Oolite seems to have most nearly resembled the flora of New Zealand,—a flora remarkable for the great abundance of its ferns, and its vast forests of coniferous trees, that retain at all seasons their coverings of acicular spiky leaves. It is to this flora that Dacrydium cupressinum,—so like a club moss in its foliage,—belongs; and Podocarpus ferrugineus,—a tree which more closely resembles in its foliage the Eathie conifer, save that its spiky leaves are somewhat narrower and longer than any other with which I am acquainted. About two thirds of the plants which cover the plains, or rise on the hill-sides of that country, are cryptogamic, consisting mainly of ferns and their allies; and it is a curious circumstance,—which was, however, not without precedent in the merely physical conditions of the Oolitic flora of Scotland,—that so shallow is the soil even where its greatest forests have sprung up, and so immediately does the rock lie below, that the central axes of the trees do not elongate downwards into a tap, but throw out horizontally on every side a thick network of roots, which rises so high over the surface as to render walking through the woods a difficult and very fatiguing exercise. The flora of the Oolite, like that of New Zealand, seems to have been in large part cryptogamic, consisting of ferns and the allied horse-tail and club moss families. Its forests seem to have contained only cone-bearing trees; at least among the many thousand specimens of its fossil woods which have been examined, no tissue of the true, dicotyledonous character has yet been found; and with the exception of the leaves just described, all those yet found in the System, which could have belonged to true trees, are of the acicular form common to the Coniferæ, and show in their dense ligneous structure that they were persistent, not deciduous. Nor is there evidence wanting that many of the Coniferæ of the period grew in so shallow a soil, that their tap-roots were flattened and bent backwards, and they were left to derive their sole support, like the trees of the New Zealand forests, from such of their roots as shot out horizontally. We even know the nature of the rock upon which they rested. As shown by fragments still locked up among the interstices of their petrified roots, it was an Old Red flagstone similar to that of Caithness in the neighborhood of Wick and Thurso, and containing the same fossil remains. In the water-rolled pebbles of the Conglomerate of Helmsdale and Port Gower,—pebbles encrusted by Oolitic corals, and enclosed in a calcareous paste, containing Oolitic belemnites and astreæ,—I have found the well marked fishes and fucoids of the Old Red Sandstone. As shown by the appearance of the rounded masses in which these lay, they must have presented as ancient an appearance in the times of the Lower Oolite as they do now; and the glimpse which they lent of so remote an antiquity, through the medium of an antiquity which, save for the comparison which they furnished the means of instituting, might be well deemed superlatively remote, I have felt singularly awe-inspiring and impressive. Macaulay anticipates a time when the traveller from some distant land shall take his stand on a broken arch of London Bridge to survey the ruins of St. Paul's. In disinterring from amid the antique remains of the Oolite the immensely more antique remains of the Old Red Sandstone, I have felt as such a traveller would feel if, on setting himself to dig among the scattered heaps for memorials of the ruined city, he had fallen on what had been once the Assyrian Gallery of the British Museum, and had found mingling with the antiquities of perished London the greatly older and more venerable antiquities of Nineveh or of Babylon. The land of the Oolite in this northern locality must have been covered by a soil which,—except that from a lack of the boulder clays it must have been poorer and shallower,—must have not a little resembled that of the lower plains of Cromarty, Caithness, and Eastern Ross. And on this Palæozoic platform, long exposed, as the Oolitic Conglomerates abundantly testify, to denuding and disintegrating agencies,—a platform beaten by the surf where it descended to the sea level, and washed in the interior by rivers, with here a tall hill or abrupt precipice, and there a flat plain or sluggish morass,—there grew vast forests of cone-bearing trees, tangled thickets of gigantic equisetaceæ, numerous forms of Cycas and Zamia, and wide-rolling seas of fern, amid whose open spaces club mosses of extinct tribes sent forth their long, creeping stems, spiky and dry, and thickly mottled with pseudo-spore-bearing catkins.
The curtain drops over this ancient flora of the Oolite in Scotland; and when, long after, there is a corner of the thick enveloping screen withdrawn, and we catch a partial glimpse of one of the old Tertiary forests of our country, all is new. Trees of the high dicotyledonous class, allied to the plane and the buckthorn, prevail in the landscape, intermingled, however, with dingy funereal yews; and the ferns and equisetæ that rise in the darker openings of the wood approach to the existing type. And yet, though eons of the past eternity have elapsed since we looked out upon Cycas and Zamia, and the last of the Calamites, the time is still early, and long ages must lapse ere man shall arise out of the dust, to keep and to dress fields waving with the productions of yet another and different flora, and to busy himself with all the labor which he taketh under the sun. Our country, in this Tertiary time, has still its great outbursts of molten matter, that bury in fiery deluges many feet in depth, and many square miles in extent, the debris of wide tracts of woodland and marsh; and the basaltic columns still form in its great lava bed; and ever and anon, as the volcanic agencies awake, clouds of ashes darken the heavens, and cover up the landscape as if with accumulated drifts of a protracted snow storm. Who shall declare what, throughout those long ages, the history of creation has been? We see at wide intervals the mere fragments of successive floras; but know not how what seem the blank interspaces were filled, or how, as extinction overtook in succession one tribe of existences after another, and species, like individuals, yielded to the great law of death, yet other species were brought to the birth, and ushered upon the scene, and the chain of being was maintained unbroken. We see only detached bits of that green web which has covered our earth ever since the dry land first appeared; but the web itself seems to have been continuous throughout all time; though ever as breadth after breadth issued from the creative loom, the pattern has altered, and the sculpturesque and graceful forms that illustrated its first beginnings and its middle spaces have yielded to flowers of richer color and blow, and fruits of fairer shade and outline; and for gigantic club mosses stretching forth their hirsute arms, goodly trees of the Lord have expanded their great boughs; and for the barren fern and the calamite, clustering in thickets beside the waters, or spreading on flowerless hill slopes, luxuriant orchards have yielded their ruddy flush, and rich harvests their golden gleam.
THE END.