We shall have presently to say a little more about the vegetation; but for the present we need only say that it was very different from the vegetation with which most of us are familiar. Imagine a hot, damp atmosphere, a kind of perpetual warm fog through which the rays of the sun struggled with difficulty, and where rain fell on most days of the year--a perpetual steaming hothouse. There was little variety in the appearance of the vast forest swamps. It certainly possessed, wrote Louis Figuier, the advantage of size and rapid growth; but how poor it was in species--how uniform in appearance! No flowers yet adorned the foliage or varied the tints of the forests. Eternal verdure clothed the branches of the Ferns, the Lycopods (club mosses), and Equiseta, which composed to a great extent the vegetation of the age. The forests presented an innumerable collection of individuals, but very few species, and all belonging to the lower types of vegetation. No fruit appeared fit for nourishment; none would seem to have been on the branches. Suffice it to say that few land animals seem to have existed yet; while the vegetable kingdom occupied the land, which at a later period was more thickly inhabited by air-breathing animals. A few winged insects gave animation to the air while exhibiting their variegated colours; and many mollusca (such as land-snails) lived at the same time. Ultimately all this richness of vegetation became by decay, by compression, by submergence, perhaps by being buried under earthquake movements and volcanic outbreaks, converted into coal; and we may now ask how long did this process take. A vigorous growth of vegetation has been estimated to yield annually about one ton of dried vegetable matter per acre, or 640 tons to the square mile. If this annual growth of vegetable matter were all preserved for 1000 years, and compressed till it was as dense and heavy as coal, it would form a layer about seven inches thick. But a large portion of the vegetable matter even in peat bogs escapes as gas in the making of coal. Four-fifths of it escapes in this way. If this be true the seven-inch layer would be reduced to less than one and a half inches, and a layer a foot in thickness would require between 8000 and 9000 years. The aggregate thickness of coal is frequently as much as 100 feet (when all the thicknesses of the seams are added together), and sometimes as much as 250 feet. At the foregoing rate of accumulation periods ranging from 1,000,000 to 2,500,000 years would be needed for the accumulation of such thicknesses of coal. It must be borne in mind that much depends on the rate of growth of Carboniferous vegetation, which may have been, and probably was, much more rapid than any we know outside tropical forests. On the other hand, we have been speaking of the aggregate thickness of the coal beds only. The greater part of the coal-bearing strata consists of shale and sandstone with layers or seams of coal like streaky bacon. Of the