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In the last chapter we have seen that the seams of coal, whether bituminous or anthracitic, are derived from the same species of plants, and Goppert has ascertained that the remains of every family of plants scattered through the shales and sandstones of the coal-measures are sometimes met with in the pure coal itself a fact which adds greatly to the geological interest of this flora.
Trigonocarpum olivaeforme, Lindley, with its fleshy envelope. Hooker, be referred, like the Sternbergia, to the Coniferae. Its geological importance is great, for so abundant is it in the coal-measures, that in certain localities the fruit of some species may be procured by the bushel; nor is there any part of the formation where they do not occur, except the under-clays and limestone.
These Virginian coal-measures are composed of grits, sandstones, and shales, exactly resembling those of older or primary date in America and Europe, and they rival, or even surpass, the latter in the richness and thickness of the coal-seams. One of these, the main seam, is in some places from 30 to 40 feet thick, composed of pure bituminous coal.
When such fine vegetable sediment is mixed, as is often the case, with clay, it becomes similar to the bituminous limestone and calcareo-bituminous shales of the coal-measures.
By another, the shale of the coal-measures has been indurated, assuming the character of flinty slate; and in another place the slate-clay of the lias has been changed into flinty slate, which still retains numerous impressions of ammonites. It might have been anticipated that beds of coal would, from their combustible nature, be affected in an extraordinary degree by the contact of melted rock.
Agassiz handled all specimens with the greatest care, and naturally had little patience with clumsiness; the following incident illustrates both his kindly spirit and his self-restraint. At one of the lectures he had handed down for inspection a very rare and costly fossil, from the coal-measures, I think; including the matrix, it had about the size and shape of the palm of the hand.
The popular legend is that the English, when they were compelled to abandon Guyenne, set fire to these coal-measures with the motive of doing all the mischief they could before leaving. Such fables are handed down from generation to generation. All the evil that happened to the region in the dim past is placed to the account of the English.
The coal-field of Westphalia has lately come into prominence in connection with the search which has been made for coal in Kent and Surrey, the strata which are mined at Dortmund being thought to be continuous from the Bristol coal-field. Borings have been made through the chalk of the district north of the Westphalian coal-field, and these have shown the existence of further coal-measures.
We may assume that the reptile which left these prints on the ancient sands of the coal-measures was an air-breather, because its weight would not have been sufficient under water to have made impressions so deep and distinct.
It is the rough argillaceous sandstone that accompanies the coal-measures in this part of Wales, and a moderate force gives it quite a rocking motion, which can be easily continued with one hand. It stands nearly in equilibrium upon a pivotal rock beneath.
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