Page:Popular Science Monthly Volume 23.djvu/70

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Such formations are of frequent occurrence in the coal-measures, in alternation with the seams of coal and the marine deposits left by the overflow of the sea, and this was doubtless their origin. The fossil forests which have been discovered in the same regions may be similarly accounted for. The trees growing around the perimeters of the lagoons would be partially submerged by the overflowing water, and the sections of them buried in its muddy deposit would be left to decay and fossilize in it. The persistent root-stocks of the sigillarias and calamites, unharmed by the flood, would send up new aërial stems; and most of the other plants, having the power of sending out adventitious roots from their trunks, would be able to live and continue to grow by that means, leaving their old lower parts to die, while they lifted themselves, as it were, bodily up with the ascensional movement of the soil. Several examples of such successive emissions of roots are figured in the "Mémoire." M. Grand' Eury has assumed that the concurrence of two principal circumstances, acting coincidently and in combination with each other, contributed essentially to the formation of coal. One was the transportation by water for short distances of all the vegetable matter of a region to be spread out flat and stratified at the bottom of the lagoon destined to receive it; the other was the exposure of the matter, previous to this process, in the open air to a certain amount of decay, of the nature and effects of which he has made a patient analysis. From these principles he has deduced a theory which may be summarized thus: The water which served as the vehicle for the vegetable matter, which must have been perfectly clean, because it was free from all mud, strong enough to carry along its drift, and plentiful enough to sweep all the points of the wooded region, could not have been any other than rain-water shed upon slopes pronounced enough to make it easy for it to run and carry the vegetable residues along with it, yet level enough not to allow the ground to be cut up. The land over which the water flowed must have been covered with a mass of plants and accumulated fragments abundant enough to furnish much flotsam matter, and matted enough to prevent its eroding the subjacent soil. The water must have been intermittent, else the fallen trunks of trees and the fragments of every kind which lay scattered over the ground would not have had time to undergo the partial decomposition and disaggregation of their tissues which necessarily preceded complete submersion. There must have been, then, if not real seasons, intervals of relative calm, in which the decomposition could have taken place, to be succeeded by times of protracted and extremely violent precipitation. The fact that a transportation and deposition of the parts took place is attested by the stratified structure of the coal. In both the coal and the schisto-carbonaceous laminæ, all of the fragments, down to the most delicate isolated organs, are always, with only the rarest exceptions, spread out flat, and cemented one over another, lying together like the leaves of