"double-fin;" the osteolepis, or "bony-scale;" the asterolepis, or "star-scale;" and the holoptychius, or "all-wrinkle," so

2

3

1, Acanthodes; 2, Climatius; 3, Diplacanthus.-Forfarshire.

called from the wrinkle-like sculpturing that adorns its large enamelled scales. The majority of these fishes are small, or of moderate size; and even the largest of them, the holoptychius and asterolepis, do not greatly, if at all, exceed the dimensions of a full-grown cod-fish. Nor would they startle by their forms, were they recalled to take their place among existing fishes. The little armed bull-head of our own shores is encased in as marvellous, and even more highly ornamented armour than the cephalaspis; the ostracion, or trunk-fish of the Indian ocean, is encased in a bony box, as curiously fabricated as that of the pterichthys or coccosteus; the spines of the balistes and sea-snipe are as formidable weapons as the ichthyodorulites of the diplacanth; and the scales of the bony-pike of South America, or the polypterus of the Nile, glitter with enamel, and are as quaintly sculptured as those of the osteolepis or holop

tychius of the old red sandstone. Wonderful they are, as all God's works are wonderful! but to dwell, as is too often the case, on these ancient denizens of the deep as something unusually strange and marvellous, is neither the way to forward the interests of science, nor to teach the popular mind a just appreciation of the world that surrounds it.

Turning next to the higher order of reptiles, we have as yet no undoubted instance of their existence, though footprints, bones, teeth, and scutes, unquestionably reptilian, have been detected in the sandstones of Elgin— sandstones till recently regarded as Devonian, but whose relations have lately been questioned; first, on account of the obscurity of their stratigraphical relations to the surrounding old red sandstone of the district; and, second, on account of the affinity of their reptilian remains to those occurring in true triassic strata. Partaking in the doubt, both on lithological and paleontological grounds, that the place of these Elgin sandstones may yet be found to belong to the dawn of the triassic, and not to the close of the Devonian, epoch, we have transferred the small lizard-like telerpeton, and the large "drop-scaled" crocodilian staganolepis, to the newer era-a transposition already approved by some of our leading palæontologists. It is thus that palæontology often corrects the first impressions of physical geology, and in this instance conformably so with all that we know of the reptilian life of the carboniferous era, where forms more lowly and fish-like in their character alone make their appearance. In the mean time, therefore, the existence of reptiles during the old red sandstone epoch must be held as problematical, and palæontology constrained to date their advent with the commencement of the carboniferous era. If it shall be ultimately found that these Elgin sandstones are of true Devonian age, the occurrence of reptiles having such high affinities as lizards and crocodiles, will

G

once more correct the hasty generalisations of limited observation, and teach us how vain it is to dogmatise on the rise and order of life from the imperfect data which geology has yet at her command.

Such is the hurried glance at the life of the Devonian epoch. As yet we are almost in total ignorance of its terrestrial flora and fauna. We are like voyagers to whom some unknown land looms in the distance through the seafogs and grey of the morning. Here and there a few gleams of light fall on hill-sides green with ferns and club-mosses; and as the mists roll away we catch a passing glimpse of some river-mouth fringed with reeds and rushes. This, however, is all-the interior is obscured from our vision, and no drift of fruit or forest-growth tells of a higher flora. As we coast along, we almost think we catch the reflection of glacier and icebergs, which would indicate in some regions a sterility and dearth of vegetation; but this may be a delusion, and only the sparkle of the quartzy cliffs that are broken into fragments by the surf that dashes against them. When we turn to the ocean, the view is somewhat nearer and clearer. In the warmer seas, corals of various form and beauty are rearing their reefs; shell-fish of every grade, though not of great numerical abundance, are busy along shore and in mid-water; fishes of widely different forms swarm in shoals —generically few, but individually most numerous; whilst crustaceans of uncouth shape and gigantic growth feed on the tide-borne garbage of the muddy creeks and shallow lagoons. This is all: and much as has been made of it, all reason forbids us to accept it as more than the merest contribution to the biology of the period.

Succeeding the old red sandstone, and much more sharply defined-physically and vitally-comes the great CARBOWe have now extensive alterations

NIFEROUS FORMATION.

ว

in the distribution of land and water-shallower seas-larger rivers and estuaries-wide, far-stretching swampy lands; and with these, new ocean-currents, a more genial and equable climate, and, as a concomitant, a more exuberant exhibition, and over wider areas, of vegetable and animal life. In some regions, but by no means over. the whole world, the transition from the one period to the other seems to have taken place through convulsive energy; and hence, in these regions comparatively few of the forms of the eld red sandstone survive, or pass into the carboniferous era. As in every other period, the new forms come slowly and gradually on the stage, attain their "culminating point," or period of greatest variety, size, and numbers, and then gradually or quickly decline, according to the continuity of the conditions by which they are surrounded. In the vegetable world we have now a most exuberant Flora—so exuberant that it is but faintly paralleled by the rankest growth of the tropical jungle. To account for this extraordinary development of plant-life, over such wide and diversely situated regions of the globe, various hypotheses have been offered, such as a larger percentage of carbonic acid gas in the atmosphere-the greater effect of the earth's central heat-change in the earth's axis of rotation, so as to bring the coal-bearing areas within the tropics-and greater eccentricity of the earth's orbit, so as to have brought the globe periodically nearer to the sun's influence; but as we have not in the mean time* a shadow of proof for such abnormal causes, and much evidence to the contrary, we are bound by sound induction to seek for the explanation in

*We say in the mean time; for the recurrence of colder and warmer cycles over the northern hemisphere, as evinced by the geological record, is clearly the result of some great cosmical law, depending either on telluric or on solar influences, and, as such, must sooner or later be satisfactorily determined.--See Concluding Chapter-" The Law," Section 6.

the then peculiar distribution of sea and land, in the altitude of its shores, in the arrangement of warmer aërial and oceanic currents, and generally in a concentration of these conditions, such as would produce the necessary climate. And, after all-as in the case of the great tertiary elephants and rhinoceroses of Northern Europe, whose representatives are now found only in the tropics—we know too little of the nature of the plants to say under what conditions of climate they would attain their greatest exuberance, though we clearly perceive from their foliage and mode of growth that it was at once equable and continuous.* Generally speaking, we find them resembling equisetums, marshgrasses, reeds, club-mosses, tree-ferns, and coniferous trees; and these in existing nature attain their maximum development in warm-temperate and subtropical, rather than in equatorial regions. The Wellingtonias of California, and the pines of Norfolk Island, are more gigantic than the largest coniferous tree yet discovered in the coal-measures; the tree-ferns of New Zealand luxuriate in humid and shady spots; the tussack of Falkland Island, and the phormium of New Zealand, show leaves as broad and long as the poacites of the carboniferous period; while accumulations of peat-growth are the products of coldly-temperate, rather than of equatorial latitudes. Besides all this, we have coal-beds in other formations-the oolite, the Wealden, and tertiary; and if we are to go in search of abnormal conditions for the production of the one, we must admit the existence of similar causes for the production of the other— an admission, as we shall afterwards see, that would lead to

* It is more than likely, as suggested by the late Robert Brown, that many of the Coal-plants were inhabitants of the swamp and shallow waters-estuarine and marine; and that, rooted in mud, rich in organic matters, and surrounded by water of an equable and genial temperature, they enjoyed the conditions at once of a rapid and of a gigantic growth.