siderations 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 ha