LECTURE ELEVENTH. ON THE LESS KNOWN FOSSIL FLORAS OF SCOTLAND.* PART I. SCOTLAND has its four fossil floras, -its flora of the Old Red Sandstone, its Carboniferous flora, its Oolitic flora, and that flora of apparently Tertiary age of which his Grace the Duke of Argyll found so interesting a fragment overflown by the thick basalt beds and trap tuffs of Mull. Of these, the only one adequately known to the geologist is the gorgeous flora of the Coal Measures, probably the richest, in at least individual plants, which the world has yet seen. The others are all but wholly unknown; and the Association may be the more disposed to tolerate the comparative meagreness of the few brief remarks which I purpose making on two of their number, -the floras of the Old Red Sandstone and the Oolite, - from the consideration that that meagreness is only too truly representative of the present state of our knowledge regarding them; and that if my descriptions be scanty and inadequate, it is only because the facts are still few. How much of the lost may *The substance of this and the following lecture was originally given in a single paper, before the Geological Section of the British Association, held at Glasgow in September 1855. So considerable have been the additions, however, that the one paper has swelled into two lectures. Most of the added matter was at first thrown into the form of Notes; but it was found, that from their length and frequency, they would have embarrassed the printer, mayhap the reader also; and so most of the larger ones have been introduced into the text within brackets. yet be recovered I know not; but the circumstance that two great floras, - remote predecessors of the existing one, which once covered with their continuous mantle of green the dry land of what is now Scotland, should be represented by but a few coniferous fossils, a few cycadaceous fronds, a few ferns and club mosses, must serve to show what mere fragments of the past history of our country we have yet been able to recover from the rocks, and how very much in the work of exploration and discovery still remains for us to do. We stand on the further edge of the great floras of by-past creations, and have gathered but a few handfuls of faded leaves, a few broken branches, a few decayed cones. The Silurian deposits of our country have not yet furnished us with any unequivocal traces of a terrestrial vegetation. Professor Nicol of Aberdeen, on subjecting to the microscope the ashes of a Silurian anthracite which occurs in Peeblesshire, detected in it minute tubular fibres, which seem, he says, to indicate a higher class of vegetation than the algæ; but these may have belonged to a marine vegetation notwithstanding. I detected some years ago, in the Trilobite-bearing schists of Girvan, associated with graptolites of the Lower Silurian type, a vegetable organism somewhat resembling the leaf of one of the pond weeds, — an order of plants, some of whose species, such as Zostera, find their proper habitats in salt water. I have placed beside this specimen a fragment of the same graptolitebearing rock, across which I have pasted part of a leaf of Zostera marina, the only plant of our Scottish seas which is furnished with true roots, bears real flowers inclosed in herbaceous spathes, and produces a well formed farinaceous seed. It will be seen, that in the few points of comparison which can be instituted between forms so exceedingly simple, the ancient very closely resembles the recent organism. It is not impossible, therefore, that the Silurian vegetable may have belonged to some tribe of plants allied to Zostera, and if so, we can easily conceive how the Silurian anthracite of our country may be altogether of marine origin, and may yet exhibit in its microscopic tubular fibres vestiges of a vegetation higher than the algæ. [It were well, in dealing with the very ancient floras, in which equivocal forms occur that might have belonged to either the land or the sea, to keep in view those curious plants of the present time, the habitats of which are decidedly marine, but which are marked by many of the peculiarities of the seed-bearing plants of the land. The superiority of Zostera to the common sea weeds of our coasts appears to have struck in the north of Scotland eyes very little practised in such matters, and seems to have given rise, in consequence, to a popular myth. Zostera marina abounds on a series of sand banks, partially 66 - uncovered by the larger stream tides, which lie directly opposite the town of Cromarty, near the spot pointed out by tradition as the site of an earlier town, which was swept away some two or three hundred years ago by the encroachments of the sea. And these banks, with their thick covering of green Zostera, used to be pointed out by the fishermen of the place, in my younger days, as the meadows of the old town, still bearing their original coverings of vegetation, a vegetation altered no doubt by the sea change" that had come over it, but still essentially the same, it was said, as that which had smiled around the old burgh, and not at all akin to the brown kelp or tangle that every storm from the boisterous north-east heaps along the shore. It was virtually affirmed that the luxuriant terrestrial grasses of ancient Cromarty had made a virtue of necessity in their altered circumstances; and that, settling down into grasses of the sea, they remained to testify that an ancient Cromarty there had once been. Zostera marina, like most plants of the land, ripens its seeds towards the close of autumn; and I have seen a smart night's frost at this season, when coincident with a stream tide that laid bare the beds, nip its seed-bearing stems by thousands; and have found them strewed along the beach a few days after, with all their grass-like spikes fully developed, and their grain-like seeds charged with a farinaceous substance, which one would scarce expect to find developed in the sea. In the higher reaches of the Cromarty Frith, the Zostera beds, which are of great extent, are much frequented, during the more protracted frosts of a severe winter, by wild geese and swans, that dig up and feed upon the saccharine roots of the plant. The Zostera of the warmer latitudes attain to a larger size than those of our Scottish seas. "A southern species," says Loudon, "Zostera oceanica, has leaves a foot long and an inch broad. It is used as a thatch, which is said to last a century; bleaches white with exposure; and furnishes the rush-like material from which the envelops of Italian liquor flasks are prepared." The simple rectilinear venation of ribbon-like fronds, usually much broken, that occurs in the Lower Old Red Sandstone, has often reminded me of that exhibited by this exotic species of Zostera.] Associated with the earliest ichthyic remains of the Old Red Sandstone, we find vegetable organisms in such abun dance, that they communicate often a fissile character to the stone in which they occur. But, existing as mere carbonaceous markings, their state of keeping is usually so bad, that they tell us little else than that the antiquely |