CHAPTER IX. LAND AND SEA GLACIERS-AVALANCHES-LAND-SLIPS AND MOUNTAIN-FALLS-EARTHQUAKES-VOLCANOES-CAUSES AND USES OF VOLCANIC ACTIONGEYSERS-SPRINGS-RIVERS-CATARACTS-LAKES-TORRENTS FLOODS-SEA EROSION-ELEVATIONS AND SUBSIDENCES OF DRYLAND AND SEA-BOTTOM-THE OCEAN. In the preceding chapter, we have dealt with the firm parts of the world's surface; and in this we shall deal with the shifting parts. And we begin with glaciers. These are slowly descending fields of viscous or slightly liquid ice. They commence at the snow-line of mountains which possess a great area within the altitudes of perpetual frost. They are formed and fed by the slow liquefaction and subsequent congelation of decending snow-masses; and may be regarded as offsets of the perpetual snow-fields, creeping down the hollows and declivities of the mountains. They move at no quicker a rate than from twelve to thirty feet in the year; but they move with prodigious power, tearing up the ground, transporting great blocks of rock, carrying everything before them, and even traversing the bottom of a glen, and forcing their prow some little way up the opposite acclivity; and they are believed by many geologists to have been the agents of some great changes on the surface of the globe. At least four hundred large ones occur in the regions of the Alps. These are the grandest glaciers in the world. They vary in length from three to thirty miles, and in thickness from one hundred to six hundred feet, but rarely have an extreme breadth of more than two miles. When seen from sufficiently elevated spots at a distance, they look like tumultuous torrents, suddenly arrested and solidified in their headlong rush down the sinuosities of their bed. Their entire mass is rent in all directions by profound fissures. Their upper parts have a whitish colour and a wildly rugged surface. Their middle parts display a gloriously blue tint sometimes passing into green, and are knobbed and pinnacled and turreted with numerous isolated ice-blocks of the most fantastic shapes. Their lower parts have the same bright cerulean hue as the middle parts, and undulate rapidly down like wavily flowing rivers. And their sides, and sometimes portions of their interior, are surmounted by walls and cliffs of ice occasionally sixty feet or upwards in height, and usually beset with masses of rock. How strongly suggestive are these glaciers of the silent power and allimmersing glory of the Upholder of the universe! Well may we exclaim with Coleridge, in his Hymn before Sunrise in the Vale of Chamouni, "Ye ice-falls! ye that from the mountain's brow Who made you glorious as the gates of Heaven God! let the torrents, like a shout of nations, God! sing ye meadow streams, with gladsome voice! And in their perilous fall shall thunder God!" The glaciers sometimes invade cultivated tracts, and pass into near juxtaposition or immediate contact with grass-lands, corn-fields, orchards, and the habitations of men. The "silent cataracts" literally blend in very limited landscape with the "pine groves" and the "meadow-streams." But they do not always descend harmlessly; for such as creep down declivities terminating in precipices occasionally fling off masses of sufficient bulk to do havoc upon anything which happens to be in the vicinity of their fall. A singular instance of this occurred in 1819, in the valley of Visp in Valais. A piece fell from a lofty precipice into that valley of so great size as to cover an area of one thousand feet in breadth and two thousand four hundred feet in length, to the depth of one hundred and fifty feet. In the neighbourhood of the place stood the village of Kanda; and the mere gust of wind produced by the fall destroyed the village, overthrowing the houses, breaking down a massive steeple, carrying away some roof-beams to the distance of nearly a mile, and whirling off millstones from the ground to a slope several yards above where they lay. Snow avalanches, however, are vastly more destructive, and are a chief class of the sublimities and terrors of alpine regions. Those which are persistent enough to slide in one sheet, descend with little noise, yet sometimes make lodgments in the valleys which seri M ously alter the climate, and do not melt away for several summers, and sometimes also uproot small forests, overwhelmn flocks, and destroy villages. In 1749, one came silently down in the night on all the village of Rucras in the canton of the Grisons; and the inhabitants, on awakening in the morning, remained awhile ignorant of what had happened, and simply felt surprise that the day did not break. Sixty of them breathed well and long enough through the interstices of the snow to be afterwards dug out alive. Drift avalanches, or those which consist of loose snow, are more tremendous by far than the sliding ones. They often descend from vast heights, and in prodigious masses, and with awful velocity. They were long supposed to be set agoing by even the most trivial vibrations of the air,-such as those arising from the tinkling of a bell or the foot-fall of a traveller; but they are now known to originate in violent gusts of wind striking suddenly against the upper altitudes of the mountains, and unaccompanied by any current in the valleys. The first moving masses are sometimes very large, and often launched off with furious impetus; and, even when small and gentle, they rarely fail to drive before them an accumulation of bulk and force which comes roaring down like an orchestra of cataracts and thunders. The mere compression of air, or sudden local squall, produced by some of these avalanches is strong enough to uproot the largest trees, to fracture rocks, and to scatter houses like chaff. We naturally pass from avalanches to land-slips and mountain-falls; but shall first glance at the curious phenomenon of travelling bogs. A notable instance of this occurred, in the summer of 1821, in the barony of Kilcoursey in Ireland. The bog had a depth of about forty feet, and an area of about five hundred acres, and was situated on a gentle slope, overlooking a narrow vale. The lower part of it was pulpy, and suffered a pressure of water from above, and suddenly broke bounds, and began to move away with the whole superstrata. The bog, once in motion, travelled with surprising speed down the slope and along the vale, and drove before it large slices several feet thick of coarse meadow-ground which lay in its way, turning them over and heaving them along like the surging of sea-billows. It was arrested for some time by a hill; but it eventually got round this, and went off at a right angle from its original course. Though twice arrested by subsequent obstacles, it surmounted them also; and continued to march so menacingly onward, that prompt and powerful engineering operations had to be performed to bring it to a halt. Land-slips, in most instances, are caused by the loosening or wearing action of percolating water upon under-strata of sand or gravel. A singular one occurred a few years ago on the slope of a high conical hill in the state of Vermont, in North America; and, among other curious effects, carried a set of farmoffices, without injury, from their own farm into the grounds of a neighbouring proprietor. A gentleman, who was transacting business in the dwelling-house with the farmer at the time when it happened, thus graphically describes it:-"As we were in the act of reading over some papers preparatory to their being signed by us, we were startled by a sudden explosion. Our first impression was, that a piece of artillery had been dis |