Page:Popular Science Monthly Volume 14.djvu/104

94 rocky beds, and through the avenues of least resistance, sometimes fusing together into solid seas amid the mountains, elsewhere stealing in sinuous and gleaming currents to the plains beneath. These solid masses, fastened like inexorable wedges into the mountain-clefts, possess motion, moving like a river, faster at the top than at the bottom, in the centre than along the sides, and in curves fastest upon the long curve; they, like rivers, also perform the offices of transportation and erosion. Long lines of fragments, detached by frost or avalanche, cover their surfaces in medial and lateral moraines, whose collected masses are poured over the glacier's extremity, where in stream or river it ends its course. Immense heaps of débris thus indicate, at the mountain's foot, the accumulated waste of its substance through the years of the glacier's slow and perpetual advance, and also record, as they lie beyond the present wall of the glacier, the past periods of its greatest extension. They grind the beds they pass over, the walls of their stony vaults are polished and inscribed, and the bowlders brought in contact with their stupendous powers of attrition are rubbed into brilliant surfaces and scored with rigid lines. Thus advancing, crevassed, convulsed, and rent into gaping chasms, loaded with blocks of stone, the glaciers are grinding down the everlasting hills and lowering the proud summits of their birthplace to the plain. Imagine half a hemisphere covered by a universal glacier whose powers of abrasion and transportation are proportionately enlarged: will not the appearances we are attempting to explain be adequately accounted for by so tremendous an agent? Let us turn to contemporaneous glaciers of the Alps and elsewhere for an answer. In mentioning characteristic instances of glacial action the glaciers are referred to by name only, as our space does not permit their reference to appropriate groups. The Glacier des Bois, as it projects its frozen tongue like a crystal wedge within the valley of Chamouni, reveals the mass of débris it has dragged down with it from the sides of Mont Blanc, in a high and rocky moraine over whose eminence the glacier pours its broken and shattered columns. In 1820 this glacier reached its frigid finger among the cultivated fields of neighboring villages, and in its slow retreat left an enormous bowlder perched upon a slope, and tracts of fragments spread in stony desolation up to the doors of the threatened hamlets. The Glacier of Tacconay has similarly withdrawn to its recesses, but strewed along the path of its former progress groups of bowlders which reach beyond the Arne. The rocks about are polished and furrowed, hillocks have been moulded into roches moutonnées, and upon their summits huge blocks deposited.

Seven thousand feet above the sea, upon the Col de Bellevue, erratic blocks are found, where no tidal force could ever have brought them, and these mingle with the present moraine of the Glacier de Bionassay, so that, as Forbes remarks, "it is impossible to say where the erratic phenomenon ends and where the glacial phenomenon begins." The Glacier