In the United States there are about 120,000 square miles underlaid by known workable coal-beds, besides what yet remains to be discovered; while on the cliffs of Nova Scotia the coal-seams can be seen one over the other for many hundred feet, and showing how the coal was originally formed.  With this immense stock of fuel in the cellars of the earth, it seems evident that we need not trouble our minds or be anxious as to the duration of our coal supply.  Besides, the conversion of vegetable matter into coal seems to be going on even now.  In the United States there are peat-bogs of considerable extent, in which a substance exactly resembling cannel coal has been found; and in some of the Irish peat-beds, as also in the North of Scotland, a similar substance has been discovered, of a very inflammable nature, resembling coal.

Yes! what could have produced this singular-looking, black, inflammable rock?  How many times was this question asked before Science could return an answer?  This she can now do with confidence.  Coal was once growing vegetable matter.  On the surface of the shale, immediately above the coal, you will find innumerable impressions of leaves and branches, as perfect as artist ever drew.  But how could this vegetable matter ever accumulate in such masses as to make beds of coal of such vast extent, some not less than 30 feet thick?  It would take 10 or 12 feet of green vegetable matter to make 1 foot of solid coal.  Let us transport ourselves to the carboniferous times, and see the condition of the earth, and this may assist us to answer the question.  Stand on this rocky eminence and behold that sea of verdure, whose gigantic waves roll in the greenest of billows to the verge of the horizon—­that is a carboniferous forest.  Mark that steamy cloud floating over it, an indication of the great evaporation constantly proceeding.  The scent of the morning air is like that of a greenhouse; and well it may be, for the land of the globe is a mighty hothouse—­the crust of the earth is still thin, and its internal heat makes a tropical climate everywhere, unchecked by winter’s cold, thus forcing plants to a most luxurious growth.

Descend, and let us wander through this forest and examine it more closely.  What strange trees are here!  No oaks, no elms, or ash, or chestnut—­no trees that we ever saw before.  It looks as if the plants of a boggy meadow had shot up in a single night to a height of 60 or 70 feet, and we were walking among the stalks—­a gigantic meadow of ferns, reeds, grasses, and club-mosses.  A million columns rise, so thick at the top that they make twilight at mid-day, and their trunks are so close together we can scarcely edge our way between them, whilst the ground is carpeted with trailing plants completely interwoven.  What strange trees they are!  Beneath us lies an accumulation of vegetable matter more than 200 feet in thickness—­the result of the growth and decay of plants in this swamp for