CARBONACEOUS DEPOSITS. 153 



Opposed to the idea of floating rafts is, the enormous thickness they nmsx 

 have attained, to have produced beds of coal such as are known, between 

 two layers of arena'ceous matter. In fact, taking into consideration the 

 specific weight of wood, the amount of carbon it contains relatively to that 

 of carbona'ceous deposits, we find that the latter can only be twenty-two 

 hundreds, or even seven hundreds (according to the kind of plants), of 

 the primitive volume of the mutters which gave origin to them. Besides, 

 estimating the numerous voids left by the irregular interlacing of these 

 debris in a raft, we know that coal, tor example, which is formed of the 

 lightest plants, as the equisita'ceae, ferns, &,c., cannot be, in the bed, more 

 than thirty-five thousands of the thickness of the raft that formed it : that 

 is, a coal-bed of from one or two to thirty yards thick, would require the 

 rafts to have been twenty-eight or fifty-seven, to eight hundred and fifly- 

 seven yards in thickness, which evidently exceeds the limits of probability, 

 and in most seas would be impossible. 



The idea of the formation being analogous to that of peat-bogs does not 

 present this difficulty, arid only requires time for the accumulation of the 

 necessary organic materials. In the present state of things, this time would 

 be very considerable; for, according to the calculation of M. de Beaumont, 

 on the quantity of carbon annually produced by our forests, not much more 

 than six-tenths of an inch in thickness of coal would be ibrmed, in carbo- 

 na'ceous deposits, in the period of a century. But everything leads to the 

 belief, that at a mean temperature of 71 (Fahrenheit), when the atmosphere 

 was filled with vapour, and vegetation, in the genera of plants that then 

 grew in our country, was infinitely more vigorous than at present: we are 

 also Jed to believe that at the epoch of these formations, when the earth had 

 not yet cooled to its present temperature, a great deal of carbonic acid 

 issued from its interior, and the appropriation of the carbon by plants was 

 then more rapid. It is not only for the formation of coal that a long period 

 of time is required ; all sedimentary and calcareous deposits formed only of 

 shells, which acquire much greater thickness than carbona'ceous deposits, 

 have certainly required many centuries to reach this point. 



The hypothesis which assimilates deposits of coal to peat-bogs, is fortified 

 by the different characters they present; such are, not only the trees found 

 erect with their roots, and the remarkable preservation of the leaves in 

 schists, but the deposition in isolated basins, of greater or less extent, seems" 

 to indicate swamps and marshy places formed in depressions of the surface 

 of the soil. These deposits are often surrounded on all sides by rocks of an 

 anterior formation, which form the parietes of the cavity where they took 

 place ; frequently, we also find that a certain number of small basins, inde- 

 pendent of each other, forming part of a more extensive basin of a species 

 of lake filled with contemporaneous arena'ceous matters, on the surface of 

 which there would be formed as many masses of combustible. There are 

 some, too, that extend through the length of certain ancient valleys, and are 

 contained in them. All these circumstances are observable in the deposits 

 of the centre and south of France ; but in the north of France, in Belgium, 

 in England, and in Scotland, it is different. There, the beds of combustible 

 seem to extend over great spaces; and the assemblage of facts, as well as 

 the immediate superposition of marine limestone, found in all these countries, 

 leads us to suppose that these deposits, now dislocated and separated by seas, 

 have once formed part of the same whole. It was not in swamps or in 

 closed lakes they were formed, but in a vast sea, the receptacle of all the 

 debris of the vegetation of its coasts and islands, that they must have taken 

 place, and in which undulatory motion stratified these materials as well as 

 all other sedimentary deposits. 



Certain deposits of lignite were evidently formed in the same manner a* 

 coal ; but there are others which constitute irregular masses of wood thrown 



