"The true coal," says Dr. Dawson, "consists principally of the flattened bark of Sigillarioid and other trees, intermixed with leaves of Ferns and Cordaites, and other herbaceous débris, and with fragments of decayed wood, constituting 'mineral charcoal,' all these materials having manifestly alike grown and accumulated where we find them.

Further, the Sigillarioe grew on the same soils which supported Conifers, Lepidodendra, Cordaites, and Ferns-plants which could not have grown in water.

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.

Calamodendron (5 specimens) 82.95 4.78 11.89 0.48 2. Cordaites (4 specimens) 82.94 4.88 11.84 0.44 3. Lepidodendron (3 specimens) 83.28 4.88 11.45 0.39 4. Psaronius (4 specimens) 81.64 4.80 13.11 0.44 \v/ 5. Ptychopteris (1 specimen) 80.62 4.85 14.53 6.

Cordaites 42.1 57.8 Quite porous.

We know, in fact, that the wood of the Calamodendrons is composed of alternately radiating bands formed of ligneous and thick walled prosenchymatous tissue, while the wood of Cordaites, which is less dense, recalls that of certain coniferæ of the present day (Araucariæ).