(2) The place occupied by peats, lignites, and bituminous and anthracite coal in sedimentary grounds, and the organic structure that we find less and less distinct in measure as we pass from one of these combustibles to one more ancient, have given rise to the theory mentioned above, viz., that vegetable matter having, under the prolonged action of heat and moisture, experienced a greater and greater alteration, passed successively through the different states whose composition is indicated in the following table: H. C. O. N. Coke. Ashes. Density. Peat 5.63 57.03 29.67 2.09 ---- 5.58 ---- Lignite 5.59 70.49 17.2 1.73 49.1 4.99 1.2 Bitumin. coal 5.14 87.45 4 1.63 68 1.78 1.29 Anthracite 3.3 92.5 2.53 ---- 89.5 1.58 1.3 Aside from the fact that anthracite is not met with solely in the lower coal measures, but is found in the middle and upper ones, and that bituminous coal itself is met with quite abundantly in the secondary formations, and even in tertiary ones, it seems to result from recent observations that if vegetable matter, when once converted into lignites, coal, etc., be preserved against the action of air and mineral waters by sufficient thick and impermeable strata of earth, preserves the chemical composition that it possessed before burial. The coal measures of Commentry, as well as certain others, such as those of Bezenet, Swansea, etc., contain quite a large quantity of coal gravel in sandstone or argillaceous rocks. These fragments sometimes exhibit a fracture analogous to that of ordinary coal, with sharp angles that show that they have not been rolled; and the sandstone has taken their exact details, which are found in hollow form in the gangue. In other cases these fragments exhibit the aspect of genuine shingle or rolled pebbles. These pebbles of coal have not been misshapen under the pressure of the surrounding sandstone, nor have they shrunk since their burial and the solidification of the gangue, for their surface is in contact with the internal surface of their matrix. Everything leads to the belief that they were extracted from pre-existing coal deposits that already possessed a definite hardness and bulk, at the same time as were the gravels and sand in which they are imprisoned. It became of interest, then, to ascertain the age to which the formation of these fragments might be referred, they being evidently more ancient than those considered above, which, as we have seen, could not have been transported in this state on account of their dimensions and the fragility of made coal. Thanks to the kindness of Mr. Fayol, we have been enabled to make such researches upon numerous specimens that were still inclosed in their sandstone gangue and that had been collected in the coal strata of Commentry. In some of their physical properties they differ from the more recent isolated fragments and from the ordinary coal of this