In reflecting on the statement, thus briefly made, of the main facts connected with the origin of the coal formed during the carboniferous epoch, two or three considerations suggest themselves.

In the first place, the great phantom of geological time rises before the student of this, as of all other, fragments of the history of our earth—­springing irrepressibly out of the facts, like the Djin from the jar which the fisherman so incautiously opened; and like the Djin again, being vaporous, shifting, and indefinable, but unmistakably gigantic.  However modest the bases of one’s calculation may be, the minimum of time assignable to the coal period remains something stupendous.

Principal Dawson is the last person likely to be guilty of exaggeration in this matter, and it will be well to consider what he has to say about it:—­

“The rate of accumulation of coal was very slow.  The climate of the period, in the northern temperate zone, was of such a character that the true conifers show rings of growth, not larger, nor much less distinct, than those of many of their modern congeners.  The Sigillariae and Calamites were not, as often supposed, composed wholly, or even principally, of lax and soft tissues, or necessarily short-lived.  The former had, it is true, a very thick inner bark; but their dense woody axis, their thick and nearly imperishable outer bark, and their scanty and rigid foliage, would indicate no very rapid growth or decay.  In the case of the Sigillariae, the variations in the leaf-scars in different parts of the trunk, the intercalation of new ridges at the surface representing that of new woody wedges in the axis, the transverse marks left by the stages of upward growth, all indicate that several years must have been required for the growth of stems of moderate size.  The enormous roots of these trees, and the condition of the coal-swamps, must have exempted them from the danger of being overthrown by violence.  They probably fell in successive generations from natural decay; and making every allowance for other materials, we may safely assert that every foot of thickness of pure bituminous coal implies the quiet growth and fall of at least fifty generations of Sigillariae, and therefore an undisturbed condition of forest growth enduring through many centuries.  Further, there is evidence that an immense amount of loose parenchymatous tissue, and even of wood, perished by decay, and we do not know to what extent even the most durable tissues may have disappeared in this way; so that, in many coal-seams, we may have only a very small part of the vegetable matter produced.”

Undoubtedly the force of these reflections is not diminished when the bituminous coal, as in Britain, consists of accumulated spores and spore-cases, rather than of stems.  But, suppose we adopt Principal Dawson’s assumption, that one foot of coal represents fifty generations of coal plants; and, further, make