The Glacial Theory, 



143 



When a glacier moves, it wears and rubs the bed on which it re- 

 poses ; scratches the smoothed walls ; triturates the detached masses 

 which are interposed between the ice and the rock, and reduces them 

 to sand, or to an argillaceous paste ; rounds the blocks, which are of 

 an angular form, and which offer resistance to the pressure ; and po- 

 lishes completely those which have broad sides. At the surface of 

 the glacier, matters proceed in quite a different manner. The frag- 

 ments of rock which are detached from the neighbouring walls, and 

 which fall there, rest upon the ice, and are at most thrown out to its 

 edges. They thus advance with the glacier without being displaced, 

 or at least without being rubbed against one another, excepting those 

 which have become interposed between the rock and the ice, and 

 they arrive at the extremity of the glacier with their angles entire, 

 their edges sharp, and their surfaces irregular. Let us suppose, now, 

 that, in consequence of certain circumstances, one of those immense 

 glaciers charged with debris of rocks, such as the lower glacier of 

 the Aar, or the glacier of Zermatt, should be melted, and it would 

 result that all the angular blocks at the surface of the glacier would 

 repose on the irregular mass of rounded debris which at present lies 

 under the ice. Some of these blocks would likewise be carried to a 

 great distance on rafts of ice, if the melting were sufficiently rapid to 

 cause currents capable of floating large masses of ice charged with 

 blocks. If we suppose, on the contrary, that a glacier or a large 

 sheet of ice, like that which extends over the Col de St. Theodule, 

 were not commanded by numerous mountain peaks, then few or no 

 angular blocks would fall on its surface, but the rounded blocks 

 underneath would not the less be present. If we imagine that, in 

 such a case, particular circumstances should also occur to cause the 

 melting of the ice, there would then be found at the bottom an irre- 

 gular deposit of rounded blocks, imbedded in the more comminuted 

 materials, along with a few angular blocks above—in short, to the 

 very letter, a sort of till. In this case, again, the melting of the 

 ice would give rise to currents ; and the more considerable these 

 currents, the more they would contribute to operate farther on the 

 materials already acted on by the glaciers, whether by conveying to a 

 distance the lighter portions, and depositing them in stratification, or 

 by penetrating them more or less, and giving them a false apperance 



