1853.] SUTHERLAND ARCTIC REGIONS. 307 



pelling power continuing, a slight leaning over in the water, or yield- 

 ing motion of the whole mass, may compensate readily for being so 

 suddenly arrested. If, however, the ground be soft, so as not to 

 arrest the motion of the iceberg at once, a moraine will be the result ; 

 but the moraine thus raised will tend to bring it to a stand. We 

 can more readily conceive this from the fact that the power which 

 impels icebergs is applied to about the upper third or fourth part of 

 their whole bulk. 



Another mode of action is sometimes exhibited by the iceberg, 

 by which its triturating and ploughing force is locally brought into 

 play with immense effect. Icebergs resting on the bottom, and 

 situated at the edge of the fixed surface-ice (that which is attached 

 to the land), when pressed upon by loose and drifting floes of large 

 size, are frequently subjected to a rotatory motion, extending some- 

 times to three-fourths of a circle, or even a complete revolution. 



The conveying power of icebergs is so well known to geologists, 

 that I need make but few remarks on this subject. As a general 

 rule, the source of all the foreign matter they contain is the land 

 on both sides of the glacier. It may, however, be received from 

 other sources. I have often thought that the fragments of a huge 

 iceberg, acquiring a state of quiescence after separating into several 

 masses in one of its fearfully grand revolutions, had turned up mud 

 and other earthy matter from the bottom. This, however, is doubtful ; 

 for we can hardly conceive it possible that anything extraneous can 

 adhere to hard and brittle ice passing rapidly through the water 

 during the iceberg's revolution. Icebergs are sometimes floated so 

 close along a bold and overhanging rocky coast, as to touch the per- 

 pendicular cliffs and to remove disintegrating fragments of the rock. 

 Another, and probably the most common of these unusual modes, is 

 from coast ice, which, impelled by the winds and tides, is often 

 piled up vdth its load of rounded pebbles, sand, and mud against the 

 sides of icebergs. The foreign substances thus cast upon the surface 

 of an iceberg must necessarily be precipitated to the bottom at the 

 first revolution it undergoes. 



The quantity of rocky matter which ice is capable of floating away 

 can be estimated from the specific gravity of both substances. Taking 

 2 ".5 as the density of granite and '92 as that of ice, an iceberg half a 

 mile in breadth, a mile in length, and 200 feet high above the water 

 (dimensions, we may observe, by no means out of the average) will 

 convey a load of one hundred and forty millions tons weight. Some 

 of the icebergs seen in Davis' Straits are so charged and impregnated 

 with earthy matter, that by inexperienced persons at a distance they 

 may be mistaken for masses of solid earth. And we often obsei-ve large 

 boulders, of perhaps one hundred tons each, lying on the surface of 

 icebergs, or sometimes imbedded deeply in the ice. 



By far the greatest number of these floating masses dissolve in 

 Davis' Straits, and deposit their earthy contents throughout its extent. 

 Some of them, however, find their way into the Atlantic, and appear 

 disposed to push far to the southward into the temperate zone. As 

 Sir Charles Lyell and others hav remarked, where the greatest 



VOL. IX. — PART I. Y 



