286 GEOLOGY. [1840 



correct knowledge gained in regard to the dip of the whole 

 southern hemisphere, and the courses of the variation lines, 

 and of the intersecting lines where they approach their respec- 

 tive poles — all indispensable to the establishment of a com- 

 plete and reliable theory of terrestrial magnetism. 



(6.) It is quite evident, from the comparatively few well 

 authenticated facts so far established, that the Antarctic Con- 

 tinent is of a volcanic character, and mainly composed of 

 lava and basalt. Large masses of earth have been seen on 

 the bergs near the main shore, and boulders of granite, and 

 fragments of sand and gravel, found firmly imbedded in the 

 ice. Soundings obtained by the Peacock, too, in five and 

 eight hundred fathoms, brought up granite, red clay, and 

 dead coral. The coast outline is exceedingly bold. Bluff 

 capes and promontories jut out into the ocean, behind which 

 the land rises precipitately, peak above peak, in stupendous 

 mountain ranges, whose steep escarpments present vast icy 

 masses of crystallization, or are enveloped in perpetual snow. 



Along the coast there is a belt of field ice, with occasion- 

 ally an ice-pack, averaging about fifty miles in width. In 

 this there is but little change. Masses of ice are constantly 

 being disrupted, in the winter, by the difference in tempera- 

 ture between the air and the water, and the outer bergs are 

 sometimes driven away by the prevailing southerly winds 

 into warmer regions, where they gradually disappear. But 

 the stationary ice can scarcely be said to thaw, and congela- 

 tion is constantly talcing place to supply any deficiency. 

 Large pools of fresh water, probably rain, in sufficient abund- 

 ance to supply a navy, are often found on the tops of icebergs, 

 covered over with a thin crust of ice. 



(7.) When the icebergs are first disrupted, they are com- 

 monly of a tabular formation ; but after they have been for 

 a long time exposed to the action of the waters and the occa- 

 sional heat of the sun, they present greater irregularities, 

 and frequently assume the most fanciful appearances.* Wide 



* Icebergs one-third of a mile in length, and from one hundred and filly tJ 

 two hundred feet high, are frequently seen, in the high southern latitudes. 



