But the fishes in this group of rocks exhibit, unquestionably, the largest amount, both in number and form, of new types. Here the sharks and sauroids appear, for the first time, not small, or attenuated in bulk, but vigorous, robust specimens of their kind, strong and expert swimmers, armed with enlarged destructive organs, and every way equipped for maintaining the due proportion of numbers, and the free trade of the ocean. Thus of the order of placoids, there are twenty-eight genera, and ninety-four species; of ganoids there are five genera, and twelve species; and sauroids enumerate thirteen genera, and twenty-four distinct and entirely new specific creations. A specimen of reptilian life has here also been detected; and what is of still greater theoretic importance, in tracing the course of creation, the immediately overlying sandstones have yielded up impressions of the winged tribes that “fly in the open firmament of heaven.” This interesting fact will, in its proper place in the order of superposition, be more fully alluded to.
The genus holoptychius, which began in the old red sandstone, again occurs in the carboniferous system, under eight new specific forms. Along with the megalichthys, afterward noticed, these constitute the two great natural families of fishes of carnivorous propensities, which give a marked character to the period. The prodigious increase of the shark-like creatures, of which not less than sixty species have been described from thousands of teeth, fins, detached vertebræ, and other fragments, is equally striking. Thus, in all, the faunæ of the carboniferous period amount to upward of a thousand species, which have been either figured or described.
In contemplating the period of creation under review, we are struck not more with the forms of life which actually existed, than with the absence of races which were afterward so abundant. No quadruped or true terrestrial animal is found so low in the series of rocks, or mixed up in any way with all this profusion of marine exuviæ. Fossil insects and indications of other winged tribes have been detected; but no bone nor foot-print of beast, or inhabitant of land, has anywhere been discovered. The fact is all-important, as showing not only a plan, but a progress and succession in the work of creation. A vegetation, so rank and luxuriant as has been traced, trees towering hundreds of feet into the sky, and branches of the densest foliage stretching on every side, was amply fitted to afford shelter and food to families of terrestrial creatures of every kind. But in the circumstance, that during this period there were repeated alternations of marine and fresh water deposits, and consequently repeated submergence and elevation of land, we see a reason why the terrestrial races were not yet called into being. Great continents, comparatively speaking, did not exist; and there was no ark of safety provided to float them over the billows. Race after race would have violently perished during every shift or subsidence of the sea bottom: and hence, until the carboniferous series was completed and a statical equilibrium established between the land and waters, few or none of the races which afterward swarmed in our plains and forests were introduced upon the scene.
Fragment of Encrinital Limestone.
CHAPTER VIII.
GEOGRAPHICAL DISTRIBUTION OF COAL—GREAT COAL FIELD OF PENNSYLVANIA, VIRGINIA AND OHIO—COAL DEPOSITS OF ILLINOIS, INDIANA AND KENTUCKY—ECONOMIC HISTORY—CONDITIONS OF FORMATION.
Considered mineralogically, and now demonstrated beyond a doubt, coal and the diamond are found to be one and the same in substance, and nearly also in their modes of formation. Newton detected the properties of the diamond in its refractive power over the rays of light, and inferred that, like amber, it was an unctuous body crystallized. In the crucible he reduced it to a state of pure carbon, burning, volatilizing, and resulting in the same elementary products as charcoal. Liebig goes a step farther, and declares the diamond to be a crystalline residuum from decayed vegetables. The action of fire could not produce the mineral, but would rather have the effect of drawing out its inflammable tendencies. “Science,” he adds, “can point to no process capable of accounting for the origin and formation of diamonds, except that of decay. And there is the greatest reason for believing that they have been formed in a liquid.” Sir David Brewster, in his beautiful optical analysis, has arrived at the same general conclusions.
Coal is also a product of vegetable decay, collected and formed in a liquid. It has not crystallized, and therefore wants the sparkle and the luster of the diamond. It retains all the carbon, and more of the hydrogen, and is in consequence infinitely more useful and valuable than even the precious gem. It is carefully incased and preserved among the rocks of the earth, and thereby in like manner akin to the glittering idol, whose true habitat has been found to be the sandstones[5] immediately overlying the carboniferous formation. Thus far the parallel can be traced between the two apparently very dissimilar and unequally prized minerals: in extent of substance and geographical distribution, the history of each stands apart.
I. The Geographical Distribution of the Coal Metals.—Our knowledge on this subject is increasing with every new geographical detail connected with the history of the earth. Until very recently the carboniferous system was supposed to be of very limited extent. The return of every vessel, engaged in a voyage of discovery or otherwise, brings tidings of some new island or continent on which it is found. The same tribes of plants and animals are everywhere observed to accompany the deposit—all presenting the same generic and often the same specific characters—and uniformly on the same great scale of development. This circumstance alone bespeaks a universal formation, when every region was capable of producing all the requisite conditions in climate, vegetables, corallines, and sea-bottom, and prepares the mind for the ready admission of the existence of the mineral in every unexplored quarter of the globe. Accordingly, all the great continents of the old world abound in coal. In Russia, the carboniferous system occupies, betwixt the Dnieper and the Don, an area of about eleven thousand square miles. India, China, and the Australian archipelago give up yearly more and more of the bituminous substance. Egypt is not destitute of the jetty mineral: for recently beds several feet thick have been discovered near Asuan, on the right bank of the Nile. The vast continent of America has it in proportion to its own vastness. And man, go where he will with the knowledge of the arts, and the diffusive blessings of religion and civilization, will always find that a wise Providence has anticipated his wants, and prepared the treasure for his use.