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society is organized for a stable earth ; its whole machinery sup- poses that, while the other familiar ele- ments of air and water are fluctuating and untrustworthy, the earth affords a foundation which is firm. Now and then this implied compact with nature is broken, and the ground trembles be- neath our feet. At such times we feel a painful sense of shipwrecked con- fidence ; we learn how very precious to us was that trust in the earth which we gave without question. If the dis- turbance be of a momentary and unim- portant kind we may soon forget it, as we forget the rash word of a friend ; if it be violent, we lose one of the sub- stantial goods ' of life, our instinctive confidence in the earth beneath our feet. Although we know as yet little con- cerning the continent of North America, our experience has taught us that it is subject to frequent earthquake shocks ; it is, therefore, worth our while to pre- pare to meet them by studying their nature, their dangers, and, so far as they exist, their remedies. In this way we shall at least escape from the fear which comes with unknown evils ; we may, perhaps, be prepared to mingle a little philosophy with the tribulations which these disturbances bring to us. The notion that the ground is naturally steadfast is an error an error which arises from the incapacity of our senses to appreciate any but the most palpable and, at the same time, most exceptional of its movements. The idea of terra firma belongs with the ancient belief that the earth was the centre of the universe. It is, indeed, by their mobil- ity that the continents survive the un- ceasing assaults of the ocean waves, and the continuous down- wearing which the rivers and glaciers bring about. Were it not that the continents grow upward, from age to age, at a rate which compensates for their erosion, there would be no lands fit for a theatre of life ; if they had grown too slowly, their natural enemies, the waves and rain, would have kept them to the ocean level ; if too fast, they would lift new surfaces into the regions of eternal cold. As it is, the incessant growth has been so well measured to the needs, that for a hundred million years, more or less, the lands have afforded the stage for prosperous life. This upward growth, when measured in terms of human ex- perience, is slow ; it probably does not exceed, on the average, one foot in three or four thousand years. The rate var- ies in times and places. Under varying conditions, as when a glacial sheet is imposed on the continent as it was, in the immediate past, on the northern part of North America a wide area of the ice-laden land sank beneath the sea, to recover its level when the depressing burden was removed. Still the ten- dency of the continents is to elevation, and even the temporary sinking of one portion of their area is probably, in all cases, compensated by uplifts on another part by which new realms are won from the sea. Copyright, 1887, by Charles Scribner's Sons. All rights reserved.