There is nothing, however small, in nature that has not its appropriate use—nothing, however insignificant it may appear to us, that has not some important mission to fulfill. The living dust that swarms in clusters about our cheese—the mildew casting its emerald tint over our preserves—the lichen and the moss wearing away the words of grief and honor engraved upon the tombs of our forefathers, have each their appropriate work, and are all important in the great economy of nature. The little moss which so effectually aroused the emotions of Mungo Park when far away from his friends and kin, and when his spirits were almost failing, may teach a moral lesson to us all, and serve to inspire us with some of that perseverance and energy to travel through life, that it did Mungo Park in his journey through the African desert. By the steady and long-continued efforts of this fragile little plant, high mountains have been leveled, which no human power could have brought from their towering heights. Adamantine rocks have been reduced to pebbles; cliffs have mouldered in heaps upon the shore; and castles and strongholds raised by the hand of man have proved weak and powerless under the ravages of this tiny agent, and become scenes of ruin and desolation—the habitations of the owl and the bat. Yet who, to look upon the lichen, would think it could do all this?—so modest that we might almost take it for a part of the ground upon which we tread. Can this, we exclaim, be a leveler of mountains and mausoleums! Contemplate its unobtrusive, humble course; endowed by nature with an organization capable of vegetating in the most unpropitious circumstances—requiring indeed little more than the mere moisture of the atmosphere to sustain it, the lichen sends forth its small filamentous roots and clings to the hard, dry rock with a most determined pertinacity. These little fibres, which can scarcely be discerned with the naked eye, find their way into the minute crevices of the stone; now, firmly attached, the rain-drops lodge upon their fronds or membranaceous scales on the surface, and filtering to their roots, moisten the space which they occupy, and the little plant is then enabled to work itself further into the rock; the dimensions of the aperture become enlarged, and the water runs in in greater quantities. This work, carried on by a legion ten thousand strong, soon pierces the stony cliff with innumerable fissures, which being filled with rain, the frost causes it to split, and large pieces roll down to the levels beneath, reduced to sand, or to become soil for the growth of a more exalted vegetation.—This, of course, is a work of time—of generations, perhaps, measured by the span of human life; but, undaunted, the mission of the humble lichen goes on and prospers. Is not this a lesson worth learning from the book of nature? Does it not contain much that we might profit by, and set us an example