The Foot-prints of the Creator

by Hugh Miller

This busy seaport town forms that special centre, in this northern archipelago, from which the structure of the entire group can be most advantageously studied. The geology of the Orkneys, like that of Caithness, owes its chief interest to the immense development which it exhibits of one formation,—the Lower Old Red Sandstone,—and to the extraordinary abundance of its vertebrate remains. It is not too much to affirm, that in the comparatively small portion which this cluster of islands contains of the third part of a system regarded only a few years ago as the least fossiliferous in the geologic scale, there are more fossil fish enclosed than in every other geologic system in England, Scotland, and Wales, from the Coal Measures to the Chalk inclusive. Orkney is emphatically, to the geologist, what a juvenile Shetland poetess designates her country, in challenging for it a standing independent of the “Land of Cakes,”—a “Land of Fish;” and, were the trade once fairly opened up, could supply with ichthyolites, by the ton and the ship-load, the museums of the world. Its various deposits, with all their strange organisms, have been uptilted from the bottom against a granitic axis, rather more than six miles in length by about a mile in breadth, which forms the great back-bone of the western district of Pomona; and on this granitic axis—fast jammed in between a steep hill and the sea—stands the town of Stromness. Situated thus at the bottom of the upturned deposits of the island, it occupies exactly such a point of observation as that which the curious eastern traveller would select, in front of some huge pyramid or hieroglyphic-covered obelisk, as a proper site for his tent. It presents, besides, not a few facilities for studying with the geological phenomena, various interesting points in physical science of a cognate character. Resting on its granitic base, in front of the strangely sculptured pyramid of three broad tiers,—red, black, and gray,—which the Old Red Sandstone of these islands may be regarded as forming, it is but a short half mile from the Great Conglomerate base of the formation, and scarcely a quarter of a mile more from the older beds of its central flagstone deposit; while an hour’s sail on the one hand opens to the explorer the overlying arenaceous deposit of Hoy, and an hour’s walk on the other introduces him to the Loch of Stennis, with its curiously mixed flora and fauna. But of the Loch of Stennis and its productions more anon.

The day was far spent when I reached Stromness: but as I had a fine bright evening still before me, longer by some three or four degrees of north latitude than the midsummer evenings of the south of Scotland, I set out, hammer in hand, to examine the junction of the granite and the Great Conglomerate, where it has been laid bare by the sea along the low promontory which forms the western boundary of the harbor. The granite here is a ternary of the usual components, somewhat intermediate in grain and color between the granites of Peterhead and Aberdeen; and the conglomerate consists of materials almost exclusively derived from it,—evidence enough of itself, that when this ancient mechanical deposit was in course of forming, the granite—exactly such a compound then as it is now—was one of the surface rocks of the locality, and much exposed to disintegrating influences. This conglomerate base of the Lower Old Red Sandstone of Scotland—which presents, over an area of many thousand square miles, such an identity of character, that specimens taken from the neighborhood of Lerwick, in Shetland, or of Gamrie, in Banff, can scarce be distinguished from specimens detached from the hills which rise over the Great Caledonian Valley, or from the cliffs immediately in front of the village of Contin—seems to have been formed in a vast oceanic basin of primary rock,—a Palæozoic Hudson’s or Baffin’s Bay,—partially surrounded, mayhap, by primary continents, swept by numerous streams, rapid and headlong, and charged with the broken debris of the inhospitable regions which they drained. The graptolite bearing grauwacke of Banffshire seems to have been the only fossiliferous rock that occurred throughout the entire extent of this ancient northern basin; and its few organisms now serve to open the sole vista through which the geological explorer to the north of the Grampians can catch a glimpse of an earlier period of existence than that represented by the ichthyolites of the Lower Old Red Sandstone.

Very many ages must have passed ere, amid waves and currents, the water-worn debris which now forms the Great Conglomerate could have accumulated over tracts of sea-bottom from ten to fifteen thousand square miles in area, to its present depth of from one to four hundred feet. At length, however, a thorough change took place; but we can only doubtfully speculate regarding its nature or cause. The bottom of the Palæozoic basin became greatly less exposed. Some protecting circle of coast had been thrown up around it; or, what is perhaps more probable, it had sunk to a profounder depth, and the ancient shores and streams had receded, through the depression, to much greater distances. And, in consequence, the deposition of rough sand and rolled pebbles was followed by a deposition of mud. Myriads of fish, of forms the most ancient and obsolete, congregated on its banks or sheltered in its hollows; generation succeeded generation, millions and tens of millions perished mysteriously by sudden death; shoals after shoals were annihilated; but the productive powers of nature were strong, and the waste was kept up. But who among men shall reckon the years or centuries during which these races existed, and this muddy ocean of the remote past spread out to unknown and nameless shores around them? As in those great cities of the desert that lie uninhabited and waste, we can but conjecture their term of existence from the vast extent of their cemeteries. We only know that the dark, finely-grained schists in which they so abundantly occur must have been of comparatively slow formation, and that yet the thickness of the deposit more than equals the height of our loftiest Scottish mountains. It would seem as if a period equal to that in which all human history is comprised might be cut out of a corner of the period represented by the Lower Old Red Sandstone, and be scarce missed when away; for every year during which man has lived upon earth, it is not improbable that the Pterichthys and its contemporaries may have lived a century. Their last hour, however, at length came. Over the dark-colored ichthyolitic schists so immensely developed in Caithness and Orkney, there occurs a pale-tinted, unfossiliferous sandstone, which in the island of Hoy rises into hills of from fourteen to sixteen hundred feet in height; and among the organisms of those newer formations of the Old Red which overlie this deposit, not a species of ichthyolite identical with the species entombed in the lower schists has yet been detected. In the blank interval which the arenaceous deposit represents, tribes and families perished and disappeared, leaving none of their race to succeed them, that other tribes and families might be called into being, and fall into their vacant places in the onward march of creation.

Such, so far as the various hieroglyphics of the pile have yet rendered their meanings to the geologist, is the strange story recorded on the three-barred pyramid of Stromness. I traced the formation upwards this evening along the edges of the upturned strata, from where the Great Conglomerate leans against the granite, till where it merges into the ichthyolitic flagstones; and then pursued these from older and lower to newer and higher layers, desirous of ascertaining at what distance over the base of the system its more ancient organisms first appear, and what their character and kind. And, embedded in a grayish-colored layer of hard flag, somewhat less than a hundred yards over the granite, and about a hundred and sixty feet over the upper stratum of the conglomerate, I found what I sought,—a well-marked bone,—in all probability the oldest vertebrate remain yet discovered in Orkney. What, asks the reader, was the character of this ancient organism of the Palæozoic basin?

As shown by its cancellated texture, palpable to the naked eye, and still more unequivocally by the irregular complexity of fabric which it exhibits under the microscope,—by its speck-like life-points or canaliculi, that remind one of air-bubbles in ice,—its branching channels, like minute veins, through which the blood must once have flown,—and its general groundwork of irregular lines of corpuscular fibre, that wind through the whole like currents in a river studded with islands,—it was as truly osseous in its composition as the solid bones of any of the reptiles of the Secondary, or the quadrupeds of the Tertiary periods. And in form it closely resembled a large roofing-nail. With this bone our more practised palæontologists are but little acquainted, for no remains of the animal to which it belonged have yet been discovered in Britain to the south of the Grampians,[3] nor, except in the Old Red Sandstone of Russia, has it been detected any where on the Continent. Nor am I aware that, save in the accompanying wood-cut, (fig. 1,) it has ever been figured. The amateur geologists of Caithness and Orkney have, however, learned to recognize it as the “petrified nail.” The length of the entire specimen in this instance was five seven eighth inches, the transverse breadth of the head two inches and a quarter, and the thickness of the stem nearly three tenth parts of an inch. This nail-like bone formed a characteristic portion of the Asterolepis,—so far as is yet known, the most gigantic ganoid of the Old Red Sandstone, and, judging from the place of this fragment, apparently one of the first.

Fig. 1.

INTERNAL RIDGE OF HYOID PLATE OF ASTEROLEPSIS.[4]

(One third the natural size, linear.)