94 THE POPULAR SCIENCE MONTHLY. 



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 bot- 

 tom, 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 debris 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, crev- 

 assed, 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 appear- 

 ances 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 in- 

 stances of glacial action the glaciers are referred to by name onl}^, 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 debris 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 re- 

 cesses, but strewed along the path of its former progress groups of 

 bowlders which reach beyond the Arne. The rocks about are pohshed 

 and furrowed, hillocks have been moulded into roches moictonnees, 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 Avhere the erratic phe- 

 nomenon ends and where the glacial phenomenon begins." The Glacier 



