'Remarks on Glaciers. 387 



never become blended, as might be supposed ; each preserves 

 its own direction and rate of progress, the line of separation 

 being the two lateral moraines, which touch each other in 

 such a manner as to form only one. However, when the pro- 

 gress of the two glaciers is very unequal, something like a 

 division of the moraine takes place, and we then see two or 

 three parallel tracks, as in the glacier of the Aar. These 

 median moraines produce the phenomena of tables des glaciers 

 on a large scale. Being placed at first in the depression 

 formed by the union of the two convex surfaces of the conti- 

 guous glaciers, and protecting the ice which they cover from 

 evaporation, they are soon elevated on a base of ice, usually 

 in the shape of an ass's back, which, however, disappears 

 where the moraine spreads out towards its extremity. (Gla- 

 cier of the Aar.) 



Let us now examine what is the action of the ice on the 

 surface which it traverses. Here, also, we find fragments of 

 rocks, which, by being pressed and ground, as if between the 

 stones of a mill, are comminuted, or arrive, in the form of 

 roimded pebbles, at the lower part, where they form the base 

 on which the extremity of the glacier, and also the terminal 

 moraine itself, usually rest. While moving along a rocky 

 alterable surface, the ice, by modifying it, produces various 

 phenomena, the principal of which are the follomng : 



It levels it by the friction, and polishes it sometimes as per- 

 fectly as could be done by the marble-cutter, cutting the fossil 

 bodies and concretions which it meets in its progress, and ex- 

 ercising its action equally upon the bottom of the bed and its 

 sides. 



It rounds off all the angles and inequalities of the ground, 

 giving them a mammiform appearance, or transforming them 

 into protuberances with rounded surfaces. (Granites of the 

 Grimsel, lapiaz of the Valais.) 



When the ground admits, it scoops out broad furrows, from 

 an inch to a foot in diameter, the length of which is in the di- 

 rection of the movement of the ice, and of these the surface is 

 equally polished, and the angles rubbed off. Here, also, might 

 be mentioned .spoon-.shaped depressions, resembling the com- 

 mencement of a furrow which has not been continued, occa- 



