Now, is it not a legitimate inference from all this, that, out of so many concurring circumstances, not one of which is similar in all respects now, a determinate effect was INTENDED to be produced, and which cannot, in the altered condition of things, be produced again? The argument is cumulative, and bears the strongest presumptive evidence on its side. The carboniferous series cannot be repeated—not for want of vegetable or animal matter, for there is a hundred times more of both at present on the surface of the earth than perhaps ever existed in any former period—but because there are so many new causes now in operation, so many changes in the relative position of sea and land, to modify its distribution and qualities, and to influence its place in the system generally, that the same conservative arrangements and chemical appliances cannot occur, nor any similar bituminous compound as a geological formation issue from Nature’s laboratory. Leonard Horner, in enumerating the difficulties connected with the formation of the coal deposit upon the theory of the whole of the matter, vegetable and earthy, being spread over the sea-bottom, says—“That the terrestrial vegetable matter, from which coal has been formed, has in very many instances been deposited in the sea, is unquestionable, from their alternations with limestones containing marine remains.” Such deposits and alternations in an estuary at the mouth of a great river are conceivable; but whether such enormous beds of limestone, with the corals and molluscs which they contain, could be formed in an estuary, may admit of doubt. But it is not so easy to conceive the very distinct separation of the coal and the stony matter, if formed of drifted materials brought into the bay by a river. It has been said that the vegetable matter is brought down at intervals, in freshets, in masses united together, like the rafts in the Mississippi. But there could not be masses of matted vegetable matter of uniform thickness, 14,000 square miles in extent, like the Brownsville bed on the Monongahela and Ohio (the Pittsburgh seam): and freshets bring down gravel, and sand, and mud, as well as plants and trees. They must occur several times a year in every river; but many years must have elapsed during the gradual deposit of the sandstones and shales that separate the seams of coal. Humboldt tells us (“Cosmos,” p. 295),—That in the forest lands of the temperate zone, the carbon contained in the trees on a given surface would not, on an average of a hundred years, form a layer over that surface more than seven lines in thickness. If this be a well-ascertained fact, what an enormous accumulation of vegetable matter must be required to form a coal-seam of even moderate dimensions! It is extremely improbable that the vegetable matter brought down by rivers could fall to the bottom of the sea in clear unmixed layers; it would form a confused mass with stones, sand, and mud.