. The testimony of the rocks; . than twenty-two different species havebeen enumerated in the British coal fields alone; and suchwas their individual abimdance, that there are great seamsof coal which seem to be almost entirely composed of theirremains. At least the ancient soil on which these seams HISTORY OF PLANTS 65 rest, and on which then* materials appear to have beenelaborated from the elements, is in many instances as thickly-traversed by their undergromid stems as the soil occupiedby our densest forests is traversed by the tangled roots ofthe trees by which it is covered ; and we often
. The testimony of the rocks; . than twenty-two different species havebeen enumerated in the British coal fields alone; and suchwas their individual abimdance, that there are great seamsof coal which seem to be almost entirely composed of theirremains. At least the ancient soil on which these seams HISTORY OF PLANTS 65 rest, and on which then* materials appear to have beenelaborated from the elements, is in many instances as thickly-traversed by their undergromid stems as the soil occupiedby our densest forests is traversed by the tangled roots ofthe trees by which it is covered ; and we often find associatedwith them in these cases the remains of no other Sigillaria were remarkable for their beautifully sculp-tured stems, various in their pattern, according to theirspecies. All were fluted vertically, somewhat like columnsof the Grecian Doric; and each flute or channel had its lineof sculpture running adown its centre. In one species {) the sculpture consists of round knobs, surrounded Fig. SIGILLARIA RENIFORMIS. (Nat. size.) by single rings, like the heads of the bolts of the ship car-penter ; in another {S. reniformis) the knobs are double,and of an oval fomi, somewhat resembUng pairs of kidneys,— a resemblance to which the species owes its name. Inanother species {S. catenulata) Avhat seems a minute chain6* 66 THE PAL^ONTOLOGICAL of distinctly formed elliptical links drops down the middleof each flute; in yet another (S. oculata) the carvings areof an oval form, and, bearing each a round impression in its Fig. 30.
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