from the face of the earth-a country more marvellous than any that even romance or poetry has ventured to portray. 29. EFFECTS OF STREAMS AND RIVERS. - In pursuance of this object I shall first take into consideration the action of running water-of streams, and rivers. I need not dwell on those meteorological causes by which the descent of moisture on the surface of the earth is regulated; but shall content myself with observing, that rivers are the great natural outlets which convey the superfluous moisture of the land into the grand reservoir, the ocean. And so exactly is the balance of expenditure and supply maintained, that all the rivers on the face of the earth, though constantly pouring their mighty floods into the ocean, do not affect its level in the slightest perceptible degree; we may therefore assume that the quantity of moisture evaporated from the surface of the sea, is exactly equal to the sum of all the water, in all the rivers in the world. But although the body of fresh-water poured by the rivers into the basin of the ocean is again displaced by evaporation, yet there is an operation silently and constantly going on, which becomes an agent of perpetual change. The rivulets which issue from the mountains are more or less charged with earthy particles, worn from the rocks and strata over which they flow their united streams in their progress towards the rivers become more and more loaded with adventitious matter; and as the power of sea. abrasion becomes greater, by the increase in the quantity and density of the mass of water, a large proportion of materials is mechanically or chemically suspended in the fluid, and carried into the If the current be feeble, much of the mud, and the larger pebbles, will be thrown down in the bed of the river-hence the formation of the alluvial plains in the valleys of the Arun, the Adur, the Ouse, and Cuckmere, in this county.* But the greater portion will be transported to the mouths of the rivers, and there form those accumulations of the fluviatile spoils of the land which constitute deltas; the finest particles, however, will be carried far into the sea, and, transported by currents and agitated by the waves, will at length be precipitated into the profound and tranquil depths of the ocean. But the waters convey not only the mud and waterworn materials of the country over which they flow: leaves, branches of trees, and other vegetable matter-and the remains of the animals that fall into the streams, with shells and other exuviæ, human remains, and works of art, are also constantly transported and imbedded in the mud, silt, and sand of the delta, some of these remains being occasionally drifted out to sea, and deposited in its bed. 30. DELTAS OF THE GANGES, AND MISSISSIPPI. -The changes here contemplated, as they are going * Sussex. on in our own island, may appear insignificant, and incapable of producing any material effect on the earth's surface; but if we trace the results in countries where these agents are now operating on a larger scale, we shall at once perceive their importance, and that time only is wanting, to form accumulations of strata, equal in extent, and of the same character with many of those ancient deposits, which will hereafter come under our observation. From experiments made with great care, it has been ascertained that the quantity of solid matter brought down by the Ganges and carried into the sea annually, is equal to 6,368,077,440 tons: in other words, to a mass of solid materials, equal in size and weight to sixty times that of the great pyramid of Egypt; the base of that stupendous structure covering eleven acres, and its perpendicular height being 500 feet.* The Burrampooter, another river in India, conveys annually as much earthy matter into the sea as the Ganges. The waters of the Indus, as the celebrated traveller, Captain Burns, informed me, are alike loaded with earthy materials. In the mighty rivers of America, the same effects are observable; the quantities of trees brought down by the Mississippi and imbedded in its deposits are almost incredible, and the basin of the sea around the embouchure of that river, is becoming shallower *Lyell's Principles of Geology. every day, by the sole agency of the operations now under consideration. In the sediments of these rivers, the animals as well as the plants of the respective countries are continually enveloped. It is therefore evident, that should these deltas become dry land, the naturalist could, by an examination of the animal and vegetable remains imbedded in the fluviatile sediments, readily determine the characters of the fauna and flora of the countries through which the rivers had flowed. We may here observe, that in tropical regions, where animal life is profusely developed, and but little under the control of man, the animal remains buried in deltas, are far more abundant than in those of European countries, which are thickly peopled, and in a high state of civilization. The enterprising, but unfortunate Lander informed me, just before he embarked on his last fatal expedition to Africa, that many parts of the Quorra, or Niger, so far as the eye could reach, teemed with crocodiles and hippopotami; and so great was their number, that he was oftentimes obliged to drag his boat on shore lest it should be swamped by these animals. But it is unnecessary for me to dwell longer on these operations; it will suffice to have shown, that by the simple effect of running water, great destruction and modification of the surface of the land are everywhere taking place; and at the same time, fluviatile deposits are forming on an extensive scale, and enveloping animal and vegetable remains. Thus, in the deltas of the rivers of this country, we find the bones and antlers of the deer, horse, and other domesticated animals, with the trunks and branches of trees and plants of our island, river and land shells, human bones, fragments of pottery and other works of art: while in those of the Ganges and the Nile, the remains of the animals and vegetables of India and of Egypt are respectively entombed. STRATA. There is one The quantity 31. FORMATION OF circumstance connected with these facts which it will be necessary here to consider. of water in streams and rivers varies considerably at different periods of the year; in the rainy season the rivers are overflowing, and the waters remarkably turbid: the depositions, therefore, must be much greater at those periods than in the summer months, when the streams are feeble, and the rivers shallow. In that part of the river affected by the tides, there is also a constant flux and reflux of the waters, and from these causes the depositions must, to a certain degree, be periodical. Accordingly we find them disposed in strata or layers, from the partial consolidation of the surface of one bed of mud, before the superincumbent layer was precipitated upon it. Thus wherever a fresh break takes place in a bank of consolidated mud, in the delta of the Nile, it is easy to trace the deposits of each successive year, by means of the lighter earth on the top of each. When a portion is taken into the hand, it separates into layers; and on closely |