The carboniferous class of rocks have all the marks of a very peculiar formation, constructed for a special purpose, and elaborated amidst an extraordinary state of things. Here we meet with vast accumulations of vegetable, calcareous, and metallic substances, for which we detect no anterior preparations. The coming on and the outgoing of the whole coal series are as distinct as they are surprising. To what are we to compare them? By what scale of time are we to adjust the terms of their growth? Proceeding upon the existing laws of nature, calculations have been made as to the rate of increase, for a year, of pure vegetable matter, over a given area. The Ganges, Nile, Amazon, Mississippi, La Plata, and the other mighty rivers of the earth, have been appealed to as to the quantities with which they are annually charged. The forests, with their load of every revolving season, have been weighed, when their decadence of leaves, fruits, branches, and all the gatherings from the flood and storm have been duly taken into account. The result is, according to this method of solving the problem, that about six hundred thousand years were occupied in the production of the whole coal series.—It must be admitted, in any attempt to reduce this number, that the violent forces of the antecedent periods cannot be admitted as data of circulation; throughout the whole of the carboniferous era, a state of repose seems to have universally prevailed. But then all the living productive powers of nature were just as violently in operation as the others were quiescent, and the result in the one case bears a proportion to the result in the other. If inorganic matter was rapidly collected by the action of violent causes, so under an extraordinary state of things, of climate, moisture, atmosphere, and other physical arrangements, organized bodies, vegetable and animal, would multiply as rapidly. A condition of nature that produced uniformity of vegetation over the entire surface of the globe, as the coal deposit everywhere manifests, and all of gigantic dimensions in every family of plants, is not merely to be denominated _tropical_, and its results calculated by a scale of existing weights and measures. In many places of the earth, even now, several harvests are reaped within the year. Who can set bounds to their number, or guess the prodigious increase, when the whole earth was covered with a flora, not only of unrivaled exuberance, but of uniform distribution nearly on every part of its surface? But a test of indisputable value, for ascertaining the rate of increase in the sandstones and shales embraced within the coal-measures, occurs in the case of those fossil trees which are so frequently found in an upright position, or but little inclined to the plane of stratification. These are numerous in every coal-field, and are often traced through several layers or beds of rock. The fossil trees of Craigleith and Granton were about fifty feet in length, and