362 SUTHERLAND, DAViS' STRAIT AND BAFFIN'S BAY. 



floes of large size, are frequently subjected to a rotatory motion, 

 extending sometimes to three-fourths of a circle, or even a complete 

 revolution. 



The conveying power of icebergs is so vv^ell 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 perpendicular cliiFs and to remove disinte- 

 grating fragments of the rock. Another, probably the most com- 

 mon, of these unusual modes of receiving debris, is from coast-ice, 

 which, impelled by the winds and tides, is often piled up with its 

 load of pebbles, sand, and mud against 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' Strait 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 observe large boulders, of perhaps one hun- 

 dred 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' Strait, 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 Tempe- 

 rate zone. As Sir Charles Lyell and others have remarked, where 

 the greatest number of these undergo dissolution there the deposi- 

 tion of rocky matter is most active, consisting of angular and 

 rounded fragments, together with sand and mud, a great part of 

 which materials are probably from sources of very opposite 

 character.* 



Coast-ice. — Ice forming on the surface of sea-water is also well 

 known as an agent of importance in conveying away to considerable 

 distances the materials of the sea-coast. With strong gales the 

 ice in the Arctic Seas is driven in upon the coasts with great force, 

 and, if the bottom about the low- water-mark is composed of loose 



See also Col. Sabine's Observations, Brit. Assoc, Rep,, Trans. Sect,, 1843. 



