69 



MISCELLANEA. 



1. On Icebergs in the Southern Hemisphere, and the Boul- 

 ders and Erratic Blocks conveyed by them. 



[In the Narrative of the United States Exploring Expedition during the years 

 1838 to 1842, by Charles Wilkes, U.S.N., Commander of the Expedition*, 

 there appear some remarks of great interest to geologists with respect to the ice- 

 bergs in the southern hemisphere. To the volumes themselves the Editor is not 

 at present able to refer, and he is indebted for the following particulars to an ex- 

 tract given in * Silliman's Journal ' for July last, where the reference to pages is 

 not given. — Ed.] 



The ice-islands form rapidly in successive horizontal layers from 

 accumulations of snovt^ assisted by the fogs. These layers are from 

 six inches to four feet in thickness ; and the icebergs were seen in 

 all stages of formation, varying from 180 to 210 feet in height, at- 

 tached to the land, and forming a straight and perpendicular wall 

 in advance of the land, for a distance of fifty miles and more to- 

 gether. 



Detached from the land, but found along the coast, the icebergs 

 were from a quarter of a mile to five miles in length. At a distance 

 of about fifty or sixty miles from land they exhibited marks of de- 

 cay, and the stratification was often inclined at a considerable angle 

 to the horizon. 



In the southern seas, these ice-islands float down as far as lati- 

 tude 60°, without being much changed by melting, since the tem- 

 perature of the sea shows but little alteration from this point to- 

 wards the pole. Further towards the equator their texture is al- 

 tered, and they rarely exhibit signs of stratification. They drift 

 rapidly westwards and north-westwards at an average rate of from 

 half to three-quarters of a mile an hour, and they are frequently 

 found between latitudes 40° and 50° S. 



Vast multitudes of boulders are imbedded in these icebergs. All 

 those observed apparently formed part of the nucleus, and were 

 surrounded by extremely compact ice, so that they appear to be 

 connected with that portion of the ice which would be the last to 

 dissolve, and they would therefore in all probability be carried to 

 the farthest extent of their range before they were let loose or de- 

 posited. 



Captain Wilkes concludes, from the abundance and drift of ice- 

 bergs, as well as from other causes, that the land near the South 

 Pole is very extensive. 



* Five volumes, with atlax. IMiiladclphia 1815. 



