Ch. XI.] SEA-BEDS FURROWED AND POLISHED. 14.7 



carried down to the coast and then floated northward on detached 

 icebergs to great distances. 



"We learn, therefore, from a study both of the arctic and antarctic 

 regions, that a great extent of land may be entirely covered throughout 

 the whole year by snow and ice, from the summits of the loftiest 

 mountains to the sea coast, and may yet send down angular erratics 

 to the ocean. We may also conclude that such land will become in 

 the course of ages almost everywhere scored and polished like the 

 rocks which underlie a glacier. The discharge of ice into the sur- 

 rounding sea will take place principally through the main valleys, 

 although these are hidden from our sight. Erratic blocks and mo- 

 raine matter will be dispersed somewhat irregularly after reaching the 

 sea, for not only will prevailing winds and marine currents govern 

 the distribution of the drift, but the shape of the submerged area will 

 have its influence ; inasmuch as floating ice, laden with stones, will pass 

 freely through deep water while it will run aground where there are 

 reefs and shallows. Some icebergs in Baffin's Bay have been seen 

 stranded on a bottom 1000 or even 1500 feet deep. In the course of 

 ages such a sea-bed may become densely covered with transported 

 matter, from which some of the adjoining greater depths may be free. 

 If, as in West Greenland, the land is slowly sinking, a large extent of 

 the bottom of the ocean will consist of rock polished and striated by 

 land-ice, and then overspread by mud and boulders detached from 

 melting bergs. But other large areas of the bed of the sea will also 

 be marked by the repeated friction of masses of floating ice, some of 

 them several miles in diameter, which, when they strand on a gently 

 shelving reef, must grate along the bottom for some distance before 

 their course is arrested. The plasticity of ice, or its capability, by 

 whatever theory explained, of moulding itself suddenly into new 

 forms under great pressure, is so remarkable, that when enormous 

 masses of it are floating, and moving at the rate of two or more miles 

 an hour, they must, on arriving at a shelving floor of rock, adapt their 

 forms to its surface, and often be forced with violence into any cavities 

 which the uneven bottom may present. Before the momentum of so 

 vast a volume of matter can be overcome, the ice, moving with what 

 may be called great velocity, when contrasted with the insensible pro- 

 gress of a glacier, must give rise to no small trituration of rock. 

 This will be the more sure to happen, because the largest bergs, by 

 their unequal rate of melting above and below water, are continually 

 capsizing, the centre of gravity often shifting ; and by such changes 

 the superficial moraines, often finnly frozen into the ice, are carried 

 down to form the base of the iceberg, and supply sand and stones for 

 polishing and scouring the ocean's floor. The submarine striae and 

 grooves may be as uniform in their direction, and as parallel as those 

 scooped out by glaciers in an inland valley ; for in the same tracts the 

 floating ice-islands will annually take the same course at correspond- 

 ing seasons of the year, being carried by similar winds and currents 



