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SECTION VII.

OPERATIONS AT PRESENT IN PROGRESS.

It is, we believe, almost generally allowed, that the commencement of the present system of things on the earth's surface does not claim a very remote antiquity that, according to one view of the question, it cannot have a date anterior to the period of man's creation as fixed by Moses, or, according to others, an earlier commencement than the epoch of the Noachian deluge. A third party, it is true, are more indefinite in their chronology, but still fix the period of the introduction of man on the earth, and the commencement of the existing epoch, within the compass of the last six thousand years.

*

It remains to be considered, then, whether there are any indications on the earth's surface to furnish data for such conjectures, and how far these are to be depended upon.

* Note VII.

The mechanical forces continually at work in the inorganic world are daily and yearly making inroads on the solid matter of the globe, and these, again, are aided by the chemical operations called into action by the multitudes of organized existences. The combined operations of these, then, must, in a long series of ages, have left obvious traces of their effects on the earth's surface; but we must call to mind that, from the very nature of these forces, the effects must be far more extensive and conspicuous in the bed of the ocean than on dry land.

Accordingly, when we strictly investigate the operations of time on the surface of the earth, we cannot help feeling a degree of astonishment at the little change which the lapse of three or four thousand years has brought about. Except in particular localities, we neither see a great extent of waste, nor a great accumulation; we see a partial mouldering down of rocks and precipices, and a slow excavation of valleys; a gradual disappearance of headlands, and a filling up of flat shores and shallow marshes; but the great features of continents and islands still remain unchanged-the same mountains on which the sages of antiquity looked, still rear their venerable summits-the same fields and meadows stretch out their ever verdant surfaces the same streams and mighty rivers flow continually down from their mountain sources. To counteract the destructive powers of nature, there are compensating operations

as steadily at work, so that the green turf, ever thus renewed, outlasts the structures of man, which, under the inevitable laws of nature, are continually crumbling into dust,

And monuments themselves memorials need.

The principal operations taking place on the surface of the earth are, the abrading effects of river courses on their channels, the accumulation of deltas at the mouths of rivers, the wearing down of promontories and headlands, and the formation of vegetable soils, especially peat moss. It has been supposed that each and all of these may afford indications of the actual and relative ages of different countries, and to a certain extent, they most undoubtedly do so. Yet, in making calculations of this nature, we must bear in mind, that the amount of disintegration will be in proportion to the impetus and constancy of the forces at work, and to the degree of hardness of the materials acted upon. Thus, some shores are of very soft materials, easily yielding to the waves, while others are so hard as to resist in a great measure any very extensive destruction. The ocean, too, after having acted with considerable force and effect on some shores for a long period, at last throws up a barrier of loose debris which shuts out its waves, and completely excludes their farther operations; tides and currents, also, interfere with the regular deposition of deltas, and circumstances take place in the course

of ages which may materially modify the impetus of rivers. Thus, the constant effect of flowing streams is to lower the level line of their courses, and consequently to lessen the velocity and force of their currents. All rivers exhibit this to a greater or less extent; the gradual lowering of the height of many waterfalls is evidently caused by the abrading force of the currents on the sides of the rocks, now many feet above the commencement of their present descents. Under these modifications, however, this subject of inquiry is an interesting one, and deserving of farther prosecution. If a collection of accurate data of this description were made, it would then be seen how far these may tend to throw light on the actual age of particular countries, or that period when the surface of the strata first became dry land, as also on the relative ages of different continents. For it is still an important desideratum to ascertain whether the great leading outlines of the continents of the earth have had a simultaneous formation, and have been afterwards partially modified and filled up by successive operations, or whether they are of very different ages, and owe their origins to causes acting at remote intervals or epochs.

Though these disintegrating forces, then, are on the whole, gradual, and some of them checked by other compensating operations, yet they are incessant, and must, in the lapse of an indefinite period,

* Note VIII.

amount to the levelling down of the present continents. Thus, the effect of rivers is, in the first place, gradually to lower their channels to a level with the ocean, into which they enter; then this ocean flows in upon the land, forming an estuary, while its tides begin to act as disintegrating forces. In the interior, from the gradual change of levels, new streams and rivers begin to cross and intersect the country; these, too, come in time to a level with the ocean, and a farther inroad of this element is caused, till, ultimately, we have an extinction of the whole dry land.

It is remarkable, however, that in no country of the globe hitherto examined has such an extreme result of disintegrating action been discovered so as to indicate the lapse of a very remote period of commencement; not even in those very old strata which are supposed to have been elevated many ages previous to the newer formations, a result which must have been very perceptible, if an extreme disparity of age exists in the different continents. To these processes, however, we have to oppose other conservative agencies. Of this kind are the almost imperceptible elevations of portions of continents which are said to take place, and which elevations are so far indicated by many curious facts,—such as the alterations of the sea level, and the existence of recent marine shells in situations now removed from all contact with the ocean; and the more obvious