deposit. They are less compact, their density is less, and a thin film of water deposited upon their surface is promptly absorbed, thus indicating a certain amount of porosity. Their fracture is dull and they are striped with shining coal, and can be more easily sliced with a razor. From a fresh fracture, we find by the lens, or microscope, that some of them are formed of ordinary coal, that is, composed of plates of variable thickness, brilliant and dull, with or without traces of organization, and others of divers bits of wood whose structure is preserved. When reduced to thin, transparent plates, these latter show us the organization of the wood of _Arthropitus, Cordaites_, and _Calamodendron_, and of the petioles of _Aulacopteris_, that is to say, of the ligneous and arborescent plants that we most usually meet with in the coal measures of Commentry in the state of impression or of coal. In a certain number of specimens the diminution in volume of the tracheæ is less than that that we have observed in the same organs of corresponding genera. The quantity of oxygen and hydrogen that they contain is greater, and seems to bring them near the lignites. We cannot attribute these differences to the nature of the plants converted into coal, since we have just seen that they are the same in the one case as in the other. Neither does time count for anything here, since, according to accepted ideas, the burial having been longer, the carbonization ought to have been more perfect, while the contrary is the case. If we admit (1) that vegetable remains alter more and more through maceration in ordinary water and in certain mineral waters; (2) that, beginning with their burial in sufficiently thick strata of clay and sand, their chemical composition scarcely varies any further; and (3) that these are important changes only as regards their physical properties, due to loss of water and compression, we succeed quite easily in learning what has occurred. In fact, when, as a consequence of the aforesaid alteration, the vegetable matter had taken the chemical composition that we find in the less advanced coal of the pebbles, it was in the first place covered with sand and protected against further destruction, and it gradually acquired the physical properties that we now find in it. At the period that channels were formed, the coal was torn from the beds in fragments, and these latter were rolled about for a time, sometimes being broken, and then covered anew, and this too at the same time as were the plants less advanced in composition that we meet with at the same level. These latter, being like them protected against ulterior alteration, we now find less advanced in carbonization (notwithstanding their more ancient origin) than the other vegetable fragments that were converted into coal after them, but that were more thoroughly altered at the time of burial.