[I have failed hitherto in finding any remains of terrestrial plant-covered surfaces in the Old Red Sandstone of Scotland, though decided traces of desiccated sub-ærial ones are not rare. Shallows and banks seem to have been numerous during the period of at least the Lower formation. The flagstones of Caithness and Orkney, and the argillaceous fish beds of Cromarty and Ross, not only abound in the ripple-marked surfaces of a shallow sea, but also in cracked and flawed planes that must have dried and split into polygonal partings in the air and the sun. The appearance of these in the neighborhood of the town of Thurso, about half a mile to the east of the river, is not a little curious. Bearing throughout the general dingy hue of the flagstones, they yet consist of alternating beds of two distinct characters and qualities. The one kind, fissile, finely grained, and sharply ripple-marked, seems to have been deposited in shallow water; the other, not fissile, but, if I may so speak, felted together so as to yield with difficulty to the hammer in any direction, and traversed by polygonal partings, filled up usually by the substance of the overlying stratum, appears to have had a different origin. The state of keeping, too, in which the ichthyic remains of these alternating beds occur is always very different. The smaller and more delicately organized fishes are never found entire, save in the fissile, finely grained beds; in the others we detect only scattered fragments; and even these, unless they belonged to the robust Asterolepis or his congeners,—which, however, in these beds they usually do,—much broken. The polygonal partings seem to indicate that these toughly-felted beds, whose very style of weathering—rough, gnarled, fretted into globose protuberances and irregular hollows—shows that it had not been formed by quiet deposition, must have had their broad backs raised for a time above the surface of the water, to be desiccated in the hot sun. And the fragmentary state of the fossils which they contain seems to point, with the roughnesses of their weathered surfaces, to some peculiarity in their origin. The recollection which they awoke in my mind with each visit I paid them for three years together, may probably indicate what that origin was. I had a relation who died more than a quarter of a century ago, who passed many years in British Guiana, in the colony of Berbice, and whose graphic descriptions of that part of South America made a strong impression upon me when a boy, and still dwells in my memory. He was settled on a cotton plantation near the coast side; and so exceedingly flat was the surrounding country, that the house in which he dwelt, though nearly two miles distant from the shore, stood little more than five feet above its level. The soil consisted of a dark gray consolidated mud; and in looking seawards from the margin of the land, there was nothing to be seen, when the tide fell, save dreary mud flats whole miles in extent, with the line of blue water beyond stretching along the distant horizon. These mud flats were much frequented by birds of the wader family, that used to come and fish in the shallow pools for the small fry that had lingered behind when the tide fell; and my cousin, a keen sportsman in his day, has told me that he used to steal upon them in his mud shoes,—flat boards attached to the soles, like the snow shoes of the higher latitudes,—and enjoy rare sport in knocking down magnificent game, such as "the roseate spoonbill" and "gorgeous flamingo." There were times, however, when the mud shoe proved of no avail, and the flat expanse remained impassable for weeks,—
"A boggy syrtis, neither sea
Nor good dry land."
The coast,—directly impinged on by the drift current, and beaten by the long roll of waves which had first begun to rise under the impulsions of the trade winds on the African coast two thousand miles away,—was much exposed to tempests; and after every fresh storm from the east, a huge bank of mud used to come rolling in from the sea, three or four feet abreast, and remain wholly impassable until, during some two or three neap tides, its surface had been exposed to a tropical sun, and partially consolidated by the heat. And then the waste would become passable as before, and the chopped and broken surface, exposed to the ordinary action of the sea, and to gradual depositions during flood, would begin to be smoothed over, and the birds would find themselves no longer safe. Now, I am inclined to think that we have here the conditions necessary to the formation of the Thurso deposits. Let us suppose, near where Thurso now stands, a wide tract of flat mud banks in a sea so shallow as to be laid dry at ebb for miles together. Let us further suppose periods of tranquil deposition or re-arrangement, during which one ripple-marked stratum is laid quietly down over another, and the fish, killed by accident, or left stranded by the evaporation of the little pools, are covered up, like the plants in a botanist's drying-book, in a state of complete entireness. Let us yet further suppose great mud banks driven by occasional tempests from the deeper water beyond, and so heaped up over these sedimentary beds as to be exposed during even the flood of neap tides to the desiccating influences of the atmosphere and the sun, until the surface has become hard as a sun-burned brick, and has chopped into polygonal partings, with wide rents between. And finally, let us suppose the whole in this state laid under water at the return of stream tides, and exposed to the ordinary sedimentary action. Does it not seem probable that the alternating beds in all their conditions would be given us by such a process? In the stratum represented by the mud bank, the stone would be of what I have termed a felted, not a fissile character; its organic remains would exist in a fragmentary and scattered state,—for, torn up from their places of original deposition, and rolled onwards in the storm-impelled mud, they could not fail to be broken up and dispersed; and further, they would be in large part those of bulky deep-sea fishes. And lastly, the surface of these beds would be polygonally cracked and flawed, and the wider cracks filled up by the substance of the overlying strata. And these overlying strata, on the other hand,—the result of a period of quiet deposition in shallow water,—would be regularly bedded, and their ichthyic remains, consisting mainly of small littoral fishes, would be preserved in a state of comparative entireness. For, however, such numerous repetitions of alternately felted and fissile ripple-marked strata as we find in the neighborhood of Thurso,—repetitions carried on for hundreds of feet in vertical extent,—we require yet another condition,—that condition of gradual subsidence in the general crust which can alone account for the fact so often pressed upon the geologist in exploring the Coal Measures, that in deposits thousands of feet in thickness, each stratum in succession had been laid down in a shallow sea.]
It is a curious circumstance, that the Old Red flagstones which lie along the southern flanks of the Grampians, and are represented by the gray stone known in commerce as the Arbroath Pavement, have not, so far as is yet known, an organism in common with the Old Red flagstones of the north. I at one time supposed that the rectilinear, smooth-stemmed fucoid, already described, occurred in both series, as the gray stones have also their smooth-stemmed, rectilinear, tape-like organism; but the points of resemblance were too few and simple to justify the conclusion that they were identical, and I have since ascertained that they were entirely different plants. The fucoid of the Caithness flagstones threw off, as I have shown, in the alternate order, numerous ribbon-like branches or fronds; whereas the ribbon-like fronds or branches of the Forfarshire plant rose by dozens from a common root, like the fronds of Zostera, and somewhat resembled a scourge of cords fastened to a handle. Contemporary with this organism of the gray flagstone formation, and thickly occupying the planes on which it rests, there occur fragments of twisted stems, some of them from three to four inches in diameter (though represented by but mere films of carbonaceous matter), and irregularly streaked, or rather wrinkled, longitudinally, like the bark of some of our forest trees, though on a smaller scale. With these we find in considerable abundance irregularly-shaped patches, also of carbonaceous matter, reticulated into the semblance of polygonal, or, in some instances, egg-shaped meshes, and which remind one of pieces of ill woven lace. When first laid open, these meshes are filled each with a carbonaceous speck; and, from their supposed resemblance, in the aggregated form, to the eggs of the frog in their albuminous envelop, the quarriers term them "puddock [frog] spawn." The slabs in which they occur, thickly covered over with their vegetable impressions, did certainly remind me, when I first examined them some fifteen years ago, of the bottom of some stagnant ditch beside some decaying hedge, as it appears in middle spring, when paved with fragments of dead branches and withered grass, and mottled with its life-impregnated patches of the gelid substance regarding which a provincial poet tells his readers, in classical Scotch, that
"Puddock-spue is fu' o' e'en,
An' every e'e 's a pu-head."[49]
Higher authorities than the quarriers,—among the rest, the late Dr. Mantell,—have been disposed to regard these polygonal markings as the fossilized spawn of ancient Batrachians; but there now seems to be evidence enough from which to conclude that they are the remains, not of the eggs of an animal, but of the seed of a plant. Such was the view taken many years ago by Dr. Fleming,—the original discoverer, let me add, of fossils both in those Upper and Middle Old Red Sandstone deposits that lie in Scotland to the south of the Grampians. "These organisms," we find him saying, in a paper published in "Cheek's Edinburgh Journal" (1831), "occur in the form of circular flat patches, not equalling an inch in diameter, and composed of numerous smaller contiguous pieces. They are not unlike what might be expected to result from a compressed berry, such as the bramble or the rasp. As, however, they are found adjacent to the narrow leaves of gramineous [looking] vegetables, and chiefly in clay slate, originally lacustrine silt, it is probable that they constituted the conglobate panicles of extinct species of the genus Junicus or Sparzanium." From specimens subsequently found by Dr. Fleming, and on which he has erected his species Parka decipiens, it seems evident that the nearly circular bodies (which in all the better preserved instances circumscribe the small polygonal ones) were set in receptacles somewhat resembling the receptacle or calyx of the strawberry or rasp. Judging from one of the specimens, this calyx appears to have consisted of five pieces, which united in a central stem, and were traversed by broad irregularly diverging striæ. And the spawn-like patches of Carmylie appear to be simply ill preserved specimens of this fruit, whatever its true character, in which the minute circular portions, divested of the receptacle and stem, had been thrown into irregular forms by the joint agency of pressure and decay. The great abundance of these organisms,—for so abundant are they, that visitors to the Carmylie quarries find they can carry away with them as many specimens as they please,—may be regarded as of itself indicative of a vegetable origin.[50] It is not in the least strange, however, that they should have been taken for patches of spawn. The large-grained spawn of fishes, such as the lump-fish, salmon, or sturgeon, might be readily enough mistaken, in even the recent state, for the detached spherical-seed vessels of fruit, such as the bramble-berry, the stone-bramble, or the rasp. "Hang it!" I once heard a countryman exclaim, on helping himself at table to a spoonful of Caviare, which he had mistaken for a sweet-meat, and instantly, according to Milton, "with sputtering noise rejected,"—"Hang it for nasty stuff!—I took it for bramble berry jam."
PARKA DECIPIENS.