AQUEOUS AGENCIES. 



63 



blocks, and confused piles of rubbish, forming terminal 

 moraines. It is by evidence of this kind that it has been 

 proved that at one time glaciers were far more extended 

 than now in regions where they still exist, and existed in 

 great power in regions where they are 110 longer found ; 

 in other words, that there was once a glacial epoch. In 

 the Alps, for example, polished, scored, moutonneed rocks 

 and perched bowlders are found on the sides of the valleys 

 far above the present level of the glacier (old glacial flood- 

 marks), (Fig. 31) ; also, smoothed, scored, moutonneed 



FIG. 31. Ideal section of a glacier bed. a, a, present level ; 6, 6, and c, c, 

 former levels. 



rock-beds and deserted terminal moraines are found far 

 beyond the present foot of the glacier. They mark the 

 former position of the foot. Behind these old terminal 

 moraines, the waters flowing from the glaciers are 

 dammed, and thus form lakes. Similar phenomena are 

 observed in regions where glaciers 110 longer exist as, for 

 example, in the Sierra and Colorado mountains. As 

 these phenomena belong to the glacial epoch, it is best to 

 describe them in connection with that subject (p. 386). 



Pot-holes in Old Glacial Beds. Pot-holes of enor- 

 mous size like great stone wells, 10-15 ft. wide and 20-30 

 ft. deep, are often found in old glacial beds. They 

 naturally excite the wonder of the inhabitants of Alpine 

 regions and are called by them " Marmites des Giants" 

 or Mortars of the Giants. They are formed not by the ice 

 but by the rushing waters of the subglacial streams, or 



