If boghead was derived from the carbonization of parts that were soluble, or that became so through maceration, and were made insoluble at a given moment by carbonization, we can understand the very peculiar aspect that this combustible presents when it is seen under the microscope. The following figures were made in order to show the details of anatomical structure that are still visible in coal, and to permit of estimating the shrinkage that the organic substance has undergone in becoming converted into coal. It is not rare in coal mines to find fragments of wood, of which a portion has been preserved by carbonates of iron and lime, and another portion converted into coal. This being the case, it was considered of interest to ascertain whether the carbonized portion had preserved a structure that was still recognizable, and, in such an event, to compare this structure with that of the portion of the specimen that was preserved in all its details by mineralization. [Illustration: 12f: FIG. 6.--_Arthropitus gallica_, St. Etienne; transverse section, X200.] Fig. 6 shows a transverse section of a specimen of _Arthropitus Gallica_ found under such conditions. The region marked c is carbonized; the organic elements of the wood-cells, tracheæ, etc., have undergone but little change in shape. Moreover, no change at all exists in the internal parts of another specimen (Fig. 8), where we easily distinguish by their form and dimensions the ligneous cells, _aa_, and the elements, _bb_, of the wood itself. [Illustration: 12h: FIG. 8.--_Arthropitus gallica_, St. Etienne; transverse section through the carbonized part.] In the region, _b_, of Fig. 6, the ligneous elements have undergone an evident change of form, and the walls have been broken. This region, already filled by petrifying salts, but not completely hardened, has not been able to resist, as the region, _a_, an external pressure, and has become more or less misshapened. As for the not yet mineralized external portion, _c_, it has completely given way under the pressure, the walls of the different organic elements have come into contact, the calcareous or other salts have been expressed, and this region exhibits the aspect of ordinary coal, while at the same time preserving a little more hardness on account of the small quantity of mineral salts that has remained in them despite the compression.