Erratic Blocks in Plains. 229 



endeavour to explain them by means of currents. How, in- 

 deed, can it be now seriously pretended that a current can 

 convey blocks in such a manner as to rub, round, and scratch 

 one set of them, without their being heaped up according to 

 their weight, and without their being covered by regular 

 beds of finer materials, while the others remained angular, 

 and retained their unequal and rough surfaces ? These dif- 

 ferences are very favourable to the glacier theory, which ex- 

 plains them in a manner that is quite natural. 



Let us return to the glaciers of the present day, and we 

 shall find in some of the phenomena presented by them the 

 greatest analogy to the arrangement of erratic blocks, as I 

 have just described it. When a glacier moves, it wears and 

 rubs the bed on which it reposes; 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 an- 

 gular form, and which offer resistance to the pressure ; and 

 polishes completely those which have broad sides. At the 

 surface of the glacier, matters proceed in quite a different 

 manner. The fragments 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 ad- 

 vance with the glacier without being displaced, or at least with- 

 out being rubbed against one another, excepting those which 

 have become interposed between the rock and the ice, and the}^ 

 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 cur- 

 rentscapable 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 



