58 M. Cluirpfntier on the Erratic Phenoitiena of (he North, 



stood, for there are still many persons who never hear the 

 word glacier, without associating with it the idea of moun- 

 tains, lofty mountains, mountains of many thousand feet in 

 height. Such individuals think that mountains are an indis- 

 pensable condition for the existence of glaciers ; but such an 

 opinion is quite erroneous. Mountains do not exercise any 

 direct influence on glaciers, except that they sometimes favour 

 the accumulation of snow drifted by the wind. It is only 

 their cold, snowy, and rainy climate which causes the for- 

 mation, development, and movement of glaciers. Now, then, 

 if from any cause a similar climate existed in a flat country, 

 were it even at the level of the sea, there would be nothing 

 to prevent glaciers from being formed and developed. Nor 

 is the declivity of the surface a necessary condition for their 

 movement ; for, as I have shewn in my Essai (§ 14), gla- 

 ciers do not move by the action of their own gravity, nor by 

 the pressure of the high neves, or upper snow ; this movement 

 being produced solely by the dilation which the ice undergoes, 

 when the water that it has absorbed by means of the capillary 

 Assures traversing its whole mass, becomes frozen. Conse- 

 quently, if a cold, snowy, and rainy climate existed during a 

 long course of years in a region forming part of a flat and 

 smooth country, and if the summer temperature were insuffi- 

 cient to cause the complete melting of the winter snows, 

 these snows would not fail to be converted into glacier. If 

 the surface of that region presented a perfectly horizontal 

 plane, the glacier, as it became developed, would extend in 

 the direction of rays from the centre to the circumference ; 

 but if the surface were inclined, that extension, and conse- 

 quently the principal movement, would take place in the 

 direction of the line of greatest inclination (Essai, § 22). 

 These considerations render it apparent, that the absence of 

 high mountains, and the presence of immense plains, in coun- 

 tries where the erratic debris of the north have been met with, 

 cannot furnish a valid objection to the glacier hypothesis. 



The change of climate supposed by the hypothesis, must 

 have occurred after the great catastrophe which has modified 

 the surface of an immense extent of the northern hemisphere, 

 and has given to the principal chain of the Alps, to the Atlas 



