The reason of the extreme difficulty in tracing the combination of these several operative causes in any given instance, is that the effective and destructive drainage by no means follows the leading fissures, but tells fearfully on the softer rocks, sweeping away inconceivable volumes of these, while fissures or faults in the harder rocks of quite primal structural importance may be little deepened or widened, often even unindicated, by subsequent aqueous action. I have, however, described at some length the commonest structural and sculptural phenomena in the fourth volume of “Modern Painters,” and I gave a general sketch of the subject last year in my lecture[161] at the Royal Institution (fully reported in the Journal de Genève of 2d September, 1863), but I have not yet thrown together the mass of material in my possession, because our leading chemists are only now on the point of obtaining some data for the analysis of the most important of all forces—that of the consolidation and crystallization of the metamorphic rocks, causing them to alter their bulk and exercise irresistible and irregular pressures on neighboring or incumbent beds.
But, even on existing data, the idea of the excavation of valleys by ice has become one of quite ludicrous untenableness. At this moment, the principal glacier in Chamouni pours itself down a slope of twenty degrees or more over a rock two thousand feet in vertical height; and just at the bottom of this ice-cataract, where a water-cataract of equal power would have excavated an almost fathomless pool, the ice simply accumulates a heap of stones, on the top of which it rests.
The lakes of any hill country lie in what are the isolated lowest (as its summits are the isolated highest) portions of its broken surface, and ice no more engraves the one than it builds the other. But how these hollows were indeed first dug, we know as yet no more than how the Atlantic was dug; and the hasty expression by geologists of their fancies in such matters cannot be too much deprecated, because it deprives their science of the respect really due to it in the minds of a large portion of the public, who know, and can know, nothing of its established principles, while they can easily detect its speculative vanity. There is plenty of work for us all to do, without losing time in speculation; and when we have got good sections across the entire chain of the Alps, at intervals of twenty miles apart, from Nice to Innspruch, and exhaustive maps and sections of the lake-basins of Lucerne, Annecy, Como, and Garda, we shall have won the leisure, and may assume the right, to try our wits on the formative question.
J. Ruskin.[162]
[From “The Reader,” November 26, 1864.]
CONCERNING GLACIERS.
Denmark Hill, November 21.
I am obliged to your Scottish correspondent for the courtesy with which he expresses himself towards me; and, as his letter refers to several points still (to my no little surprise) in dispute among geologists, you will perhaps allow me to occupy, in reply, somewhat more of your valuable space than I had intended to ask for.
I say “to my no little surprise,” because the great principles of glacial action have been so clearly stated by their discoverer, Forbes, and its minor phenomena (though in an envious temper, which, by its bitterness, as a pillar of salt, has become the sorrowful monument of the discovery it denies)[163] so carefully described by Agassiz, that I never thought there would be occasion for much talk on the subject henceforward. As much as seems now necessary to be said I will say as briefly as I can.
What a river carries fast at the bottom of it, a glacier carries slowly at the top of it. This is the main distinction between their agencies. A piece of rock which, falling into a strong torrent, would be perhaps swept down half a mile in twenty minutes, delivering blows on the rocks at the bottom audible like distant heavy cannon,[164] and at last dashed into fragments, which in a little while will be rounded pebbles (having done enough damage to everything it has touched in its course)—this same rock, I say, falling on a glacier, lies on the top of it, and is thereon carried down, if at fullest speed, at the rate of three yards in a week, doing usually damage to nothing at all. That is the primal difference between the work of water and ice; these further differences, however, follow from this first one.
Though a glacier never rolls its moraine into pebbles, as a torrent does its shingle, it torments and teases the said morain very sufficiently, and without intermission. It is always moving it on, and melting from under it, and one stone is always toppling, or tilting, or sliding over another, and one company of stones crashing over another, with staggering shift of heap behind. Now, leaving out of all account the pulverulent effect of original precipitation to glacier level from two or three thousand feet above, let the reader imagine a mass of sharp granite road-metal and paving-stones, mixed up with boulders of any size he can think of, and with wreck of softer rocks (micaceous schists in quantities, usually), the whole, say, half a quarter of a mile wide, and of variable thickness, from mere skin-deep mock-moraine on mounds of unsuspected ice—treacherous, shadow-begotten—to a railroad embankment, passenger-embankment, one eternal collapse of unconditional ruin, rotten to its heart with frost and thaw (in regions on the edge of each), and withering sun and waste of oozing ice; fancy all this heaved and shovelled, slowly, by a gang of a thousand Irish laborers, twenty miles downhill. You will conjecture there may be some dust developed on the way?—some at the hill bottom? Yet thus you will have but a dim idea of the daily and final results of the movements of glacier moraines—beautiful result in granite and slate dust, delivered by the torrent at last in banks of black and white slime, recovering itself, far away, into fruitful fields, and level floor for human life.