Fig. 12.—VEGETATION OF THE DEVONIAN.
To the left are Calamites; next to these, Leptophleum; in the centre are Lepidodendron, Sigillaria, and a Pine. Below are Psilophyton, Cordaites, Ferns, and Asterophyllites.
Amidst these trees, every open glade is filled with delicate ferns of marvellous grace and beauty; and here and there a tree-fern rears its head, crowned with its spreading and graceful leaves, and its trunk clad with a shaggy mass of aërial roots—an old botanical device, used in these ancient times, as well as now, to strengthen and protect the stems of trees not fitted for lateral expansion. Beyond this mass of vegetation, and rising on the slopes of the distant hills, we see great trees that look like pines. We cannot approach them more nearly; but here on the margin of a creek we see some drift-trunks, that have doubtless been carried down by a land flood. One of them is certainly a pine, in form and structure of its wood very like those now living in the southern hemisphere; it is a Dadoxylon. Another is different, its sides rough and gnarled, and marked with huge irregular ridges; its wood loose, porous, and stringy, more like the bark of modern pines, yet having rings of growth and a true bark of its own, and sending forth large branches and roots. It is the strange and mysterious Prototaxites, one of the wonders of the Devonian land, and whose leaves and fruits would be worth their weight in gold in our museums, could we only procure them. A solitary fragment further indicates that in the yet unpenetrated solitudes of the Devonian forests there may be other trees more like our ordinary familiar friends of the modern woods; but of these we know as yet but little. What inhabitants have these forests? All that we yet know are a few large insects, relatives of our modern May-flies, flitting with broad veined wings over the stagnant waters in which their worm-like larvæ dwell, and one species at least assuming one of the properties of the grasshopper tribe, and enlivening the otherwise silent groves with a cricket-like chirp, the oldest music of living things that geology as yet reveals to us; and this, not by the hearing of the sound itself, but by the poor remains of the instrument attached to a remnant of a wing from the Devonian shales of New Brunswick.
A remarkable illustration of the abundance of certain plants in the Devonian, and also of the slow and gradual accumulation of some of its beds, is furnished by layers of fossil spore-cases, or the minute sacs which contain the microscopic germs of club-mosses and similar plants. In the American forests, in spring, the yellow pollen-grains of spruces and pines sometimes drift away in such quantities in the breeze that they fall in dense showers, popularly called showers of sulphur; and this vegetable sulphur, falling in lakes and ponds, is drifted to the shore in great sheets and swathes. The same thing appears to have occurred in the Devonian, not with the pollen of flowering plants, but with the similar light spores and spore-cases of species of Lepidodendron and allied trees. In a bed of shale, at Kettle Point, Lake Huron, from 12 to 14 feet thick, not only are the surfaces of the beds dotted over with minute round spore-cases, but, on making a section for the microscope, the substance of each layer is seen to be filled with them; and still more minute bodies, probably the escaped spores, are seen to fill up their interstices. The quantity of these minute bodies is so great that the shale is combustible, and burns with much flame. A bed of this nature must have been formed in shallow and still water, on the margin of an extensive jungle or forest; and as the spore-cases are similar to those of the Lepidodendra of the coal-measures, the trees were probably of this kind. Year after year, as the spores became ripe, they were wafted away, and fell in vast quantities into the water, to be mixed with the fine mud there accumulating. When we come to the coal period, we shall see that such beds of spore-cases occur there also, and that they have even been supposed to be mainly instrumental in the accumulation of certain beds of coal. Their importance in this respect may have been exaggerated, but the fact of their occurrence in immense quantities in certain coals and shales is indisputable.
This is but a slender sketch of the Devonian forests: but we shall find many of the same forms of plants in the carboniferous period which succeeds. With one thought we may close. We are prone to ask for reasons and uses for things, but sometimes we cannot be satisfied. Of what use were the Devonian forests? They did not, like those of the coal formation, accumulate rich beds of coal for the use of man. Except possibly a few insects, we know no animals that subsisted on their produce, nor was there any rational being to admire their beauty. Their use, except as helping us in these last days to complete the order of the vegetable kingdom as it has existed in geological time, is a mystery. We can but fall back on that ascription of praise to Him “who liveth for ever and ever,” on the part of the heavenly elders who cast down their crowns before the throne and say, “Thou art worthy, Lord, to receive the glory, and the honour, and the might; because Thou didst create all things, and by reason of Thy will they are and were created.”
THE CARBONIFEROUS AGE.
That age of the world’s history which, from its richness in accumulations of vegetable matter destined to be converted into coal, has been named the Carboniferous, is in relation to living beings the most complete and noble of the Palæozoic periods. In it those varied arrangements of land and water which had been increasing in perfection in the previous periods, attained to their highest development. In it the forms of animal and plant life that had been becoming more numerous and varied from the Eozoic onward, culminated. The Permian which succeeded was but the decadence of the Carboniferous, preparatory to the introduction of a new order of things. Thus the Carboniferous was to the previous periods what the Modern is to the preceding Tertiary and Mesozoic ages the summation and completion of them all, and the embodiment of their highest excellence. If the world’s history had closed with the Carboniferous, a naturalist, knowing nothing further, would have been obliged to admit that it had already fulfilled all the promise of its earlier years. It is important to remember this, since we shall find ourselves entering on an entirely new scene in the Mesozoic period, and since this character of the Carboniferous, as well as its varied conditions and products, may excuse us for dwelling on it a little longer than on the others, On the other hand, the immense economic importance of the coal formation, and the interesting points connected with it, have made the Carboniferous more familiar to general readers than most other geological periods, so that we may select points less common and well-known for illustration. Popular expositions of geology are, however, generally so one-sided and so distorted by the prevalent straining after effect, that the true aspect of this age is perhaps not much better known than that of others less frequently described.