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LESSON XCIV.

The Great Dismal Swamp. LYELL.

THERE are many swamps or morasses in the eastern part of the United States, and one of the largest of these occurs between the towns of Norfolk and Weldon. We traversed several miles of its northern extremity on the railway, which is supported on piles. It bears the appropriate and very expressive name of the "Great Dismal,” and is no less than forty miles in length from north to south, and twenty-five miles in its greatest width from east to west, the northern half being situated in Virginia, the southern in North Carolina.

I observed that the water was obviously in motion in several places, and the morass had somewhat the appearance of a broad, inundated river-plain, covered with all kinds of aquatic trees and shrubs, the soil being as black as in a peat bog. The accumulation of vegetable matter going on here in a hot climate, over so vast an area, is a subject of such high geological interest, that I shall relate what I learnt of this singular morass. It is one enormous quagmire, soft and muddy, except where the surface is rendered partially firm by a covering of vegetables and their matted roots; yet, strange to say, instead of being lower than the level of the surrounding country, it is actually higher than nearly all the firm and dry land which encompasses it; and, to make the anomaly complete, in spite of its semi-fluid character, it is higher in the interior than towards its margin.

The only exceptions to both these statements are found on the eastern side, where, for the distance of about twelve or fifteen miles, the streams flow from slightly elevated but higher land, and supply all its abundant and overflowing water. Towards the north, the east, and the south, the waters flow from the swamp to different rivers, which give abundant evi

dence, by the rate of their descent, that the Great Dismal is higher than the surrounding firm ground. This fact is also confirmed by the measurements made in levelling for the railway from Portsmouth to Suffolk, and for two canals cut through different parts of the morass, for the sake of obtaining timber. The railway itself, when traversing the Great Dismal, is literally higher than when on the land some miles distant on either side, and is six to seven feet higher than where it passes over dry ground near to Suffolk and Portsmouth.

The centre of the morass seems to lie more than twelve feet above the flat country round it. If the streams, which now flow in from the west, had for ages been bringing down black fluid mire, instead of water, over the firm subsoil, we might suppose the ground so inundated to have acquired its present configuration. Some small ridges, however, of land must have existed in the original plain or basin, for these now rise like low islands in various places above the general surface. But the streams to the westward do not bring down liquid mire, and are not charged with any sediment. The soil of the swamp is formed of vegetable matter, usually without any admixture of earthy particles. We have here, in fact, a deposit of peat from ten to fifteen feet in thickness, in a latitude where, owing to the heat of the sun and length of the summer, no peat mosses like those of Europe would be looked for under ordinary circumstances.

In countries like Scotland and Ireland, where the climate is damp, and the summer short and cool, the natural vegetation of one year does not rot away during the next in moist situations. If water flows into such land, it is absorbed, and promotes the vigorous growth of mosses and other aquatic plants; and when they die, the same water arrests their putrefaction. But, as a general rule, no such accumulation of peat can take place in a country like that of Virginia, where the summer's heat causes annually as large a quantity of dead plants to decay as is equal in amount to the vegetable matter produced in one year.

There are many trees and shrubs in the region of the Pine Barrens (and the same may be said of the United States generally) which, like our willows, flourish luxuriantly in water. The juniper-trees, or white cedar, stand firmly in the softest part of the quagmire, supported by their long tap-roots, and afford, with many other evergreens, a dark shade, under which a multitude of ferns, reeds, and shrubs, from nine to eighteen feet high, and a thick carpet of mosses, four or five inches high, spring up, and are protected from the rays of the sun. When the rays are most powerful, the large cedar, and many other deciduous trees, are in full leaf.

The black soil formed beneath this shade, to which the mosses and the leaves make annual additions, does not perfectly resemble the peat of Europe, most of the plants being so decayed as to leave little more than soft black mud, without any traces of organization. This loose soil is called "sponge " by the laborers; and it has been ascertained that, when exposed to the sun, and thrown out on the bank of a canal, where clearings have been made, it rots entirely away. Hence it is evident that it owes its preservation in the swamp to moisture and the shade of the dense foliage. The evaporation continually going on in the wet, spongy soil, during summer, cools the air, and generates a temperature resembling that of a more northern climate, or a region more elevated above the level of the sea.

Numerous trunks of large and tall trees lie buried in the black mire of the morass. In so loose a soil, they are easily overthrown by winds, and nearly as many have been found lying beneath the surface of the peaty soil, as standing erect upon it. When thrown down, they are soon covered by water, and, keeping wet, they never decompose, except the sap-wood, which is less than an inch thick. Much of the timber is ob tained by sounding a foot or two below the surface, and it is sawn into planks while half under water.

The Great Dismal has been described as being highest

towards its centre. Here, however, there is an extensive lake, of an oval form, seven miles long and more than five wide; the greatest depth is fifteen feet; and its bottom, consisting of mud like the swamp, but sometimes with a pure white sand, a foot deep, covering the mud. The water is transparent, though tinged of a pale brown color, like that of our peatmosses, and contains abundance of fish. This sheet of water is usually even with its banks, on which a thick and tall forest grows. There is no beach, for the bank sinks perpendicularly, so that, if the waters are lowered several feet, it makes no alteration in the breadth of the lake.

Much timber has been cut down and carried out from the swamp by means of canals, whion are perfectly straight for long distances, with the trees on each side arching over, and almost joining their branches across, so that they throw a dark shade on the water, which of itself looks black, being colored as before mentioned. When the boats emerge from the gloom of these avenues into the lake, the scene is said to be as beautiful as fairy land."

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The bears inhabiting the swamp climb trees in search of acorns and gum-berries, breaking off large boughs of the oaks. in order to draw the acorns near to them. These same bears are said to kill hogs, and even cows. There are also wildcats,

and occasionally a solitary wolf, in the morass.

That the ancient seams of coal were produced for the most part by terrestrial plants of all sizes, not drifted, but growing on the spot, is a theory more and more generally adopted in modern times; and the growth of what is called "sponge " in such a swamp, and in such a climate as the Great Dismal, already covering so many square miles of a low, level region, bordering the sea, and capable of spreading itself indefinitely over the adjacent country, helps us greatly to conceive the manner in which the coal of the ancient carboniferous rocks may have been formed. The heat, perhaps, may not have been excessive when the coal measures originated; but the

entire absence of frost, with a warm and damp atmosphere, may have enabled tropical forms to flourish in latitudes far distant from the line.

Huge swamps in a rainy climate, standing above the level of the surrounding firm land, and supporting a dense forest, may have spread far and wide, invading the plains, like some European peat mosses when they burst; and the frequent submergence of these masses of vegetable matter beneath seas or estuaries, as often as the land sank down during subterranean movements, may have given rise to the deposition of strata of mud, sand, or limestone, immediately upon the veg etable matter. The conversion of successive surfaces into dry land, where other swamps, supporting trees, may have formed, might give origin to a continued series of coal measures of great thickness. In some kinds of coal, the vegetable texture is apparent throughout, under the microscope; in others, it has only partially disappeared; but even in this coal, the flattened trunks of trees, converted into pure coal, are occasionally met with, and erect fossil trees are observed in the overlying strata, terminating downwards in seams of coal.

LESSON XCV.

The Rising of the Waters.

JOHN GALT.

ABOUT daybreak it began to rain, and continued to pour with increasing violence all the morning; no one thought of stirring abroad who could keep within shelter. My boys and I had for task only to keep the fire at the door of the shanty brisk and blazing, and to notice that the pools which began to form around us did not become too large; for, sometimes, besides the accumulation of the rain, little streams would saddenly break out, and, rushing towards us, would have extinguished our fire, had we not been vigilant.

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