Or rocky Avon, or of sedgy Lee;
Or coaly Tyne, or ancient hallow'd Dee;
Or Humber loud, that keeps the Scythian's name;
Or Medway smooth, or royal-towered Thame."
Passing to the new world, a vast field would spread out before us: the Mississippi, the Atchafalaya, the Ohio, the St. Lawrence, the Amazon, and many other rivers that in some cases rise high among the regions of perpetual snow, and after traversing large areas of country in the temperate zone, fall into the waters of tropical seas. By studying such examples of river-action and delta-formation as are presented by these gigantic streams, we should arrive at some conception of the conditions anciently at work in producing our present coal-fields. Nor would our researches assume aught like completion until after a scrutiny of all the larger and more important rivers of the globe. Such a work could be undertaken, perhaps, only by another Humboldt. Its successful accomplishment would certainly insure the highest renown to its author, and incalculable benefits to science.
From what we have seen of the wide waste and decay everywhere in progress on the solid lands of our planet, it becomes no difficult matter to perceive what a number of agencies must be at work in the formation of a river channel. Let the reader take his stand in some wooded ravine, where the shelving rocks on either side are hung all over with verdure, and a tiny streamlet murmurs on beneath with a flow so quiet and gentle as scarcely to shake the long pendant willow branches that dip into its surface, while the polished pebbles that strew its bed lie unmoved by the rippling current that glides over them. If in the midst of such a scene the question were to arise in his mind, How came this deep, narrow ravine into existence? what answer would in all likelihood be the first to suggest itself? His eye would scan the precipitous walls of the dell, with their rocks cleft through to a depth of perchance fifty feet. It would require no great scrutiny to assure him that the beds on the one side formed the onward prolongations of those on the other, and that consequently there must have been a time ere yet the ravine existed, when these beds stretched along unbroken. Satisfied with these results, his first impulse might be to bethink him of some primeval earthquake, when the solid land rocked to and fro like a tempested sea, and broke up into great rents and yawning chasms. Into one of these clefts he might suppose the little streamlet had eventually found its way, moistening the bare and barren rocks, until at length their surface put on a livery of moss, or lichen, or liver-wort, and the birch, the alder, and the willow, found a nestling-place in their crevices. Such a view of the origin of the woody dell would be certainly a very natural one, and in some instances might be sufficiently correct, but in the present case it will not explain the phenomena. If the reader will kindly permit me to visit the locality in his company, perhaps we may be able to light upon the true explanation, and see a few appearances worthy our attention.
First, then, how can we make sure that no convulsion of nature has produced a rent in the rocks, and so helped the streamlet to a channel? a simple question that may be well-nigh as simply answered. We stand in the centre of the dell on a broad ledge of stone, round whose well-worn sides the rivulet is ever eddying onwards. The block consists of a pale sandstone lying in a bed about three feet thick, that dips gently down the stream and underlies a seam of dull, soft, blue shale, full of small shells. We trace the edge of this sandstone bed across to the left-hand side of the ravine, and away up into the precipitous cliff, till it is lost amid the ferns and brushwood. There can be no doubt, therefore, that the ledge on which we were but now standing is a continuous portion of the rocks that form the left side of the ravine. Returning again to the centre of the stream, we proceed to trace out the course of the other end of the same bed, and find that it, too, strikes across to the rocks on the right-hand side without a break or fissure, and passes up into the cliff, of which it forms a part. Clearly, then, the sandstone bed runs in an unbroken, unfissured line, from the one side to the other, and the rocks of either cliff form one continuous series. There occurs no break or dislocation, which, of course, there must have been had the ravine owed its origin to any subterranean agency. And so we come to conclude that no great cataclysm in primeval times, no yawning abyss, or gaping chasm, has had anything whatever to do with the formation of our deep sequestered dell. What then? "Whither shall we turn," you ask, "to find another agency equally grand and powerful in its operation and mighty in its results?"
Stay, gentle reader. That craving for the grand and the sublime, that hungering after cataclysms and convulsions, that insatiable appetite for upheavals, and Titanic earth-throes, and all the mightier machinery of Nature, has done no little mischief to geology. Men have reasoned that gigantic results in the physical structure of the earth must have had equally gigantic causes operating in sublime conflict and in periodic paroxysms, now heaving a mountain chain to the clouds of heaven, now swallowing up a continent in the depths of the sea. Happily such extreme notions are fast passing away, though the old tendency in a modified form still abounds. A closer scrutiny of Nature as she actually shows herself, not as theorists fancy she should be, has revealed to us that her operations are for the most part slow, gradual, and uniform, and that she oftentimes produces the mightiest results by combinations of forces that to us might seem the very emblems of feebleness and inactivity. In place of sudden paroxysms she demands only an unlimited duration of time, and with the aid of but a few of these simple, tardy agents, she will eventually effect results perchance yet more gigantic than could be accomplished even by the grandest catastrophe. Nor in thus seeking to explain the past by defining what seems the usual mode of Nature's operations in the present, do we, as is sometimes alleged, deprive them of their high poetic element. Assuredly there is something thrilling to even the calmest imagination in contemplating the results of vast and sudden upheavals, in picturing the solid crust of the earth heaving like a ground-swell upon the ocean, in tracing amid
"Crags, knolls, and mounds, confusedly hurl'd,
The fragments of an earlier world;"