bed awaiting only the proper manipulation to be converted into useful fuel at the other. That peat is formed of plants, and largely of plants that accumulate just where they grow, can be no longer questioned.

In the swamps and bayous of the moist regions of the South, pure vegetable matter, having the appearance and properties of peat, may often be found in the very act of accumulation. It frequently occurs in immense beds, and it requires no trained observation to see that, in addition to the remains of the ordinary low marsh-plants, it is made up of the ruins and refuse of swamp-loving forest-trees. Now, all about the flanks and spurs of the Rocky Mountains, with greater or less intervals, from New Mexico to far beyond the northern limits of the United States, there are found beds of coal of peculiar quality. This coal is covered up with hardened mud containing shells and bones of aquatic animals, and everything about it suggests that the coal-making materialFig. 3.—Restoration of a Lepidodendron. was somehow sunk beneath the waters of an old lake, and was buried under the gradually increasing bed of mud with which the old lake-basin was finally filled. But the point of interest is this: that in many places the Rocky Mountain coal has reached a stage of decomposition not so very much in advance of the humus and peat of our modern swamps and bayous. We might, indeed, hesitate about calling some portions of it coal at all—for the original structure is almost perfectly preserved—yet it must be admitted that for the most part the decomposition has advanced far enough to produce an article that deservedly ranks as coal. In the light of what may be observed going on in every favorably situated swamp to-day, the source of the material and the method of accumulation of the Rocky Mountain coal can hardly be doubtful. I need not weary you by leading you step by step through all the known coal-fields that illustrate the different stages in the process of coal-formation. It will be sufficient to say that a perfect gradation may be traced from the lignite, as it is called, of the Rocky Mountains to the purer and more perfect coal of the Mississippi Valley; and so, even setting aside the internal evidence of our Iowa coal, we are compelled to believe that it is simply one of the terms of the same series to which the lignite and the peat belong, and that the initial term of that series is to be looked for in the living vegetation of modern marsh and forest.

The conclusion is interesting, though to an intelligent audience it could hardly be called unexpected. The method of reaching it is worthy of notice, and points some important lessons. Though the