MECHANICAL ACTION OF GLACIERS. 153 



small white cloud in the zenith, a few acres in extent, in 

 violent internal agitation (from the hurricanes of wind 

 blowing through it), yet immovable as if fixed by some 

 spell, the material ever changing, the form and aspect 

 unvarying. The " Table-Cloth " is formed also at the com- 

 mencement of a "north-wester/' but its fringes then 

 descend on the opposite side of the mountain, which is no 

 less precipitous.' 



Other illustrations, perhaps more pertinent, are supplied 

 by sand ripples on the shore, and by the contour of sand 

 drifts, while an illustration of reboundings out at sea, like 

 to the serial rebound described in the passage cited from 

 the writings of Sir John Herschel, are supplied by banks 

 in some of the Argyleshire lochs, vertical to the line of 

 descent of the Highland glen down which in pre-Adamic 

 times poured the glacier which hollowed out the basin. 

 The confining sides of a valley once formed would elongate 

 the furrow or depression thus created in a direct rather 

 than a cross direction ; but the alternate elevations and 

 depressions, and thus the succession of pits in the thalweg 

 of the glacier, may also have been thus produced. 



In view of this it becomes more easy to see how 

 pools of such depths of water as 780 feet, 840 feet, 1,584 

 feet, 2,964 feet, 3,766 feet, and 3,980 feet, may have been 

 produced in the Sogne fiord and its branches, while the 

 depth of the sea at the mouth of the fiord is only 600 feet, 

 may have been produced, and successions of such hollows 

 in the line of the fiord and lateral branches. In alike way 

 may have been produced the basins of such lakes in the 

 interior of the country as the Miosen with a depth of 

 basin 1,110 feet below the level of the sea, corresponding 

 to the depth of the sea basin in the outer portion of the 

 Christiania fiord. 



The force with which the water of such falls as have 

 been described impinge on the basin at their base must be 

 tremendous ; but water is a liquid yielding material. 

 Imagine what must have been the impinging force of an 



