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of miles before they reach their mouths, and bear nothing to the ocean but comminuted mud and vegetable matter that is held in solution; and that they throw down almost immediately on reaching the sea. No portion of it, probably, is carried beyond the lines at which their currents are arrested by the resistance of the waters of the ocean: and that is within a very narrow circle, compared to the vast spaces that lie beyond. The result accordingly of their transporting agency is, simply, at first slowly to diminish the depth of the ocean at their mouths, and finally, gradually to extend the dry land at those points into the sea. Their influence is exhausted in the formation of their deltas. The main bed of the ocean is as completely unaffected by them as though they were not in existence. Their limited power and the narrow sphere within which their agency is circumscribed, forbid the supposition that such rivers can have been the instruments of conveying to the ocean the materials of which the strata are constituted. The area over which many of the strata extend is immense. Gneiss is generally considered as one of the most universal of the rocks, and lies very generally, it is held, between the granite which is the fundamental rock, and the fossiliferous strata. The fossiliferous strata in some of their divisions exist everywhere, except in the narrow spaces in which either granite, or some of the lowest orders of the stratified rocks, rise to the surface. In this country the New York or Silurian system, extending from the lowest of the fossiliferous rocks up to the old red sandstone, and comprising a vast series of sandstones, limestones, and shales, spreads in some of its divisions from the eastern range of the Appalachians to Lake Superior^ and from Lake Champlain to the Rocky Mountains, and forming a bed on an average many thousand feet, and in places probably several miles in thickness. The fancy that that vast mass of matter can have been borne there, and distributed in so equable a manner by rivers, is an extravagance at which common sense revolts. It is only matched in its disregard of probability, by the hypothesis that the limestone and chalk formations are the product of testaceous animals elaborated by them from other matter, of which lime is not in any appreciable measure a constituent. The effect, in the conditions that are supposed, lies wholly out of the sphere of possibility. It might as well be imagined that the granite mountains themselves that rise from beneath these strata and rear their naked summits into the sky, were floated in solid masses by streams or tides from those fabled continents, and planted in their present positions. The cause is infinitely disproportioned to the task that is assigned it. It has none of the qualities that are requisite to the production of such an effect. Sir C. Lyell, however, notwithstanding he admits that all the heavy matter borne down by a river must fall to the bottom almost immediately on its entering the sea, still maintains that the stream naturally advances the line of its deposits further into the deep, and that the change of the area, by that cause, on which its sediment is thrown down, and a transference of the river itself to a new line and point of debouchure by the elevation or inclination of the continent from which it descends, will sufficiently account for the distribution of the detritus out of which he holds the strata were formed, over the area which they occupy.

"It is only by carefully considering the combined action of all the causes of change now in operation, whether in the animate or inanimate world, that we can hope to explain such complicated appearances as are exhibited in the general arrangement of mineral masses.

"The surface of the terraqueous globe may be divided into two parts, one of which is undergoing repairs, while the other, constituting, at any one period, by far the larger portion of the whole, is either suffering degradation, or remaining stationary without loss or increment. The dry land is for the most part wasting by the action of rain, rivers, and torrents ; and part of the bed of the sea is exposed to the excavating action of currents, while the greater part, remote from continents and islands, receives no new deposits. For as a turbid river throws down all its sediment into the first lake which it traverses, so currents flowing from land or from shoals purge themselves from foreign ingredients in the first deep basin which they enter, and beyond this the blue waters of the ocean may for ages remain clear to the greatest depths.

"The other part of the terraqueous surface is the receptacle of new deposits, and in this portion alone the remains of plants and animals become fossilized. Now the position of this area, where new formations are in progress, and where alone any memorials of the state of organic life are preserved, is always varying, and must for ever continue to vary; and for the same reason that portion of the terraqueous globe, which is undergoing waste also shifts its position; and those fluctuations depend partly on the action of aqueous and partly on igneous causes.

"In illustration of these positions I now observe that the sediment of the Rhone, which is thrown into the Lake of Geneva, is now conveyed to a spot a mile and a half distant from that where it accumulated in the tenth century, and six miles from the point where the Delta began originally to form. We may look forward to the period when the Lake will be filled up, and then a sudden change will take place in the distribution of the transported matter; for the mud and sand brought down from the Alps will thenceforth be carried nearly two hundred miles southwards, where the Rhone enters the Mediterranean."—Principles of Geology, vol. ii. pp. 210, 211.

No river, however, nor rivers could ever, by that process, spread a layer of pebbles, sand, or the most comminuted mud over the whole bed of a spacious sea; nor bear any appreciable quantity of matter more than a very short distance within the deep. The current of a river on entering the sea, whether the waters of the deep are stationary, or in motion on a line that is transverse to that current, must meet a resistance that instantly checks its rapidity, and soon puts an end to its progress. All the matter accordingly borne forward by its impulse, or held in solution, must necessarily be deposited in the area within which it is circumscribed. Not a particle can ever be carried out of that limit, except by a movement of the waters of the sea that is independent of the river. It is demonstrable, therefore, that the detritus carried down by a river cannot be spread over the whole of the bed of an ocean, or spacious sea; inasmuch as it would require that the current of the river should extend over the whole of the area, and displace the whole mass of the waters of the ocean, or sea, which is as much out of the circle of possibility as it is that it should transport the solid strata themselves by its current. This part of Sir C. Lyell's theory, therefore, furnishes no solution of the diffusion over the bed of the ocean of the materials of which the strata are formed.

His supposition that it could be produced by a change of the position of the continents from which it is supposed to be drawn, causing a transferrence of

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