LIST OF WOOD-CUTS

PAGE
1.Internal ridge of hyoid plate of Asterolepis[31]
2.Shagreen of Raja clavata:—of Sphagodus[54]
3.Scales of Acanthodes sulcatus:—shagreen of Scyllium stellare[55]
4.Scales of Cheiracanthus microlepidotus:—shagreen of Spinax Acanthias[56]
5.Section of shagreen of Scyllium stellare:—of scales of Cheiracanthus microlepidotus[56]
6.Scales of Osteolepis microlepidotus:—of an undescribed species of Glyptolepis[57]
7.Osseous points Of Placoid Cranium[65]
8.Osseous centrum of Spinax Acanthias:—of Raja clavata[67]
9.Portions of caudal fin of Cheiracanthus:—of Cheirolepis[69]
10.Upper surface of cranium of Cod[72]
11.Cranial buckler of Coccosteus[74]
12.Cranial buckler of Osteolepis[75]
13.Upper surface of head of Osteolepis[77]
14.Under surface of head of Osteolepis[79]
15.Head of Osteolepis, seen in profile[80]
16.Cranial buckler of Diplopterus[81]
17.Ditto[82]
18.Palatal dart-head, and group of palatal teeth, of Dipterus[83]
19.Cranial buckler of Dipterus[85]
20.Base of cranium of Dipterus[86]
21.Under jaw of Dipterus[87]
22.Longitudinal section of head of Dipterus[88]
23.Section of vertebral centrum of Thornback[92]
24.Dermal tubercles of Asterolepis[95]
25.Scales of Asterolepis[96]
26.Portion of carved surface of scale[96]
27.Cranial buckler of Asterolepis[98]
28.Inner surface of cranial buckler of Asterolepis[99]
29.Plates of cranial buckler of Asterolepis[102]
30.Portion of under jaw of Asterolepis[103]
31.Inner side of portion of under jaw of Asterolepis[104]
32.Portion of transverse section of reptile tooth of Asterolepis[105]
33.Section of jaw of Asterolepis[106]
34.Maxillary bone?[108]
35.Inner surface of operculum of Asterolepis[109]
36.Hyoid plate[110]
37.Nail-like bone of hyoid plate[111]
38.Shoulder plate of Asterolepis[112]
39.Dermal bones of Asterolepis[113]
40.Internal bones of Asterolepis[114]
41.Ditto[115]
42.Ischium of Asterolepis[116]
43.Joint of ray of Thornback:—of Asterolepis[117]
44.Coprolites of Asterolepis[118]
45.Hyoid plate of Thurso Asterolepis[124]
46.Hyoid plate of Russian Asterolepis[127]
47.Spine of Spinax Acanthias:—fragment of Onondago spine[143]
48.Tail of Spinax Acanthius:—of Ichthyosaurus tenuirostris[172]
49.Port Jackson Shark (Cestracion Phillippi)[177]
50.Tail of Osteolepis[195]
51.Tail of Lepidosteus osseus[196]
52.Tail of Perch[197]
53.Altingia excelsa (Norfolk-Island Pine)[212]
54.Fucoids of the Lower Old Red Sandstone[216]
55.Two species of Old Red Fucoids[217]
56.Fern (?) of the Lower Old Red Sandstone[219]
57.Lignite of the Lower Old Red Sandstone[221]
58.Internal structure of lignite of Lower Old Red Sandstone[223]

STROMNESS AND ITS ASTEROLEPIS.
THE LAKE OF STENNIS.

When engaged in prosecuting the self-imposed task of examining in detail the various fossiliferous deposits of Scotland, in the hope of ultimately acquainting myself with them all, I extended my exploratory ramble, about two years ago, into the Mainland of Orkney, and resided for some time in the vicinity of Stromness.

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.)

There were various considerations which led me to regard the “petrified nail” in this case as one of the most interesting fossils I had ever seen; and, before quitting Orkney, to pursue my explorations farther to the south, I brought two intelligent geologists of the district,[5] to mark its place and character, that they might be able to point it out to geological visitors in the future, or, if they preferred removing it to their town museum, to indicate to them the stratum in which it had lain. It showed me, among other things, how unsafe it is for the geologist to base positive conclusions on merely negative data. Founding on the fact that, of many hundred ichthyolites of the Lower Old Red Sandstone which I had disinterred and examined, all were of comparatively small size, while in the Upper Old Red many of the ichthyolites are of great mass and bulk, I had inferred that vertebrate life had been restricted to minuter forms at the commencement than at the close of the system. It had begun, I had ventured to state in the earlier editions of a little work on the “Old Red Sandstone,” with an age of dwarfs, and had ended with an age of giants. And now, here, at the very base of the system, unaccompanied by aught to establish the contemporary existence of its dwarfs,—which appear, however, in an overlying bed about a hundred feet higher up,—was there unequivocal proof of the existence of one of the most colossal of its giants. But not unfrequently, in the geologic field, has the practice of basing positive conclusions on merely negative grounds led to a misreading of the record. From evidence of a kind exactly similar to that on which I had built, it was inferred, some two or three years ago, that there had lived no reptiles during the period of the Coal Measures, and no fish in the times of the Lower Silurian System.

I extended my researches, a few days after, in an easterly direction from the town of Stromness, and walked for several miles along the shores of the Loch of Stennis,—a large lake about fourteen miles in circumference, bare and treeless, like all the other lakes and lochs of Orkney, but picturesque of outline, and divided into an upper and lower sheet of water by two low, long promontories, that jut out from opposite sides, and so nearly meet in the middle as to be connected by a thread-like line of road, half mound, half bridge. “The Loch of Stennis,” says Mr. David Vedder, the sailor-poet of Orkney, “is a beautiful Mediterranean in miniature.” It gives admission to the sea by a narrow strait, crossed, like that which separates the two promontories in the middle, by a long rustic bridge; and, in consequence of this peculiarity, the lower division of the lake is salt in its nether reaches and brackish in its upper ones, while the higher division is merely brackish in its nether reaches, and fresh enough in its upper ones to be potable. Viewed from the east, in one of the long, clear, sunshiny evenings of the Orkney summer, it seems not unworthy the eulogium of Vedder. There are moory hills and a few rude cottages in front; and in the background, some eight or ten miles away, the bold, steep mountain masses of Hoy; while on the promontories of the lake, in the middle distance, conspicuous in the landscape, from the relief furnished by the blue ground of the surrounding waters, stand the tall gray obelisks of Stennis—one group on the northern promontory, the other on the south,—

“Old even beyond tradition’s breath.”

The shores of both the upper and lower divisions of the lake were strewed, at the time I passed, by a line of wrack, consisting, for the first few miles from where the lower loch opens to the sea, of only marine plants, then of marine plants mixed with those of fresh-water growth, and then, in the upper sheet of water, of lacustrine plants exclusively. And the fauna of the loch is, I was informed, of as mixed a character as its flora,—the marine and fresh-water animals having each their own reaches, with certain debatable tracts between, in which each kind expatiates with more or less freedom, according to its specific nature and constitution,—some of the sea-fish advancing far on the fresh water, and others, among the proper denizens of the lake, encroaching far on the salt. The common fresh-water eel strikes out, I was told, farthest into the sea-water; in which, indeed, reversing the habits of the salmon, it is known in various places to deposit its spawn. It seeks, too, impatient of a low temperature, to escape from the cold of winter, by taking refuge in water brackish enough, in a climate such as ours, to resist the influence of frost. Of the marine fish, on the other hand, I found that the flounder got greatly higher than any of the others, inhabiting reaches of the lake almost entirely fresh. I have had an opportunity elsewhere of observing a curious change which fresh water induces in this fish. In the brackish water of an estuary, the animal becomes, without diminishing in general size, thicker and more fleshy than when in its legitimate habitat, the sea: but the flesh loses in quality what it gains in quantity;—it grows flabby and insipid, and the margin-fin lacks always its strip of transparent fat. But the change induced in the two floras of the lake—marine and lacustrine—is considerably more palpable and obvious than that induced in its two faunas. As I passed along the strait, through which it gives admission to the sea, I found the commoner fucoids of our sea-coasts streaming in great luxuriance in the tideway, from the stones and rocks of the bottom. I marked, among the others, the two species of kelp-weed, so well known to our Scotch kelp-burners,—Fucus nodosus and Fucus vesiculosus,—flourishing in their uncurtailed proportions; and the not inelegant Halidrys siliquosa, or “tree in the sea,” presenting its amplest spread of pod and frond. A little farther in, Halidrys and Fucus nodosus disappear, and Fucus vesiculosus becomes greatly stunted, and no longer exhibits its characteristic double rows of bladders. But for mile after mile it continues to exist, blent with some of the hardier confervæ, until at length it becomes as dwarfish and nearly as slim of frond as the confervæ themselves; and it is only by tracing it through the intermediate forms that we succeed in convincing ourselves that, in the brown stunted tufts of from one to three inches in length, which continue to fringe the middle reaches of the lake, we have in reality the well-known Fucus before us. Rushes, flags, and aquatic grasses may now be seen standing in diminutive tufts out of the water; and a terrestrial vegetation at least continues to exist, though it can scarce be said to thrive, on banks covered by the tide at full. The lacustrine flora increases, both in extent and luxuriance, as that of the sea diminishes; and in the upper reaches we fail to detect all trace of marine plants: the algæ, so luxuriant of growth along the straits of this “miniature Mediterranean,” altogether cease; and a semi-aquatic vegetation attains, in turn, to the state of fullest development any where permitted by the temperature of this northern locality. A memoir descriptive of the Loch of Stennis, and its productions, animal and vegetable, such as old Gilbert White of Selborne could have produced, would be at once a very valuable and curious document, important to the naturalist, and not without its use to the geological student.

I know not how it may be with others; but the special phenomena connected with Orkney that most decidedly bore fruit in my mind, and to which my thoughts have most frequently reverted, were those exhibited in the neighborhood of Stromness. I would more particularly refer to the characteristic fragment of Asterolepis, which I detected in its lower flagstones, and to the curiously mixed, semi-marine, semi-lacustrine vegetation of the Loch of Stennis. Both seem to bear very directly on that development hypothesis,—fast spreading among an active and ingenious order of minds, both in Britain and America, and which has been long known on the Continent,—that would fain transfer the work of creation from the department of miracle to the province of natural law, and would strike down, in the process of removal, all the old landmarks, ethical and religious.