306 Analyses of Books. [Oct 



and black clay, is thrown up, and which is equal in diameter to 

 the column ejected by the great Geyser at its strongest eruptions. 

 The height of the jets varied greatly, rising on the first propul- 

 sions of the liquid to about 12 feet, and continuing to ascend, as 

 it were, by leaps till they gained the highest point of elevation, 

 which was upwards of 30 feet, when they again abated much 

 more rapidly than they rose. While Dr. Henderson continued 

 there, which was about an hour, the eruptions took place every 

 five minutes, and lasted about two minutes and a half. 



From Krabla Dr. H. proceeded to the eastern extremity of the 

 island, whence he returned to Reykiavik along the southern 

 coast ; and in so doing passed along the narrow and dangerous 

 tract, extending between the sea and the Ybkuls, or ice moun- 

 tains, which occupy the whole interior of the island in this 

 quarter. 



The Ybkuls are mountainous tracts, varying considerably in 

 elevation, almost the entire surface of which is covered with 

 snow and glaciers. Being perfectly desert, the remote parts of 

 scarcely any of them have been explored ; but where they come 

 in contact with the cultivated or inhabited districts, their mis- 

 chievous and often fatal effects are but too well known. The 

 glaciers of the Alps, according to Saussure and other accurate 

 observers, are often found to encroach somewhat on the adjacent 

 lands and then to retreat, partly in consequence of the vicissi- 

 tude of the seasons, and partly from the accumulated pressure 

 of the water from the melting of the snow filling the crevices in 

 the ice, loosening more or less its adhesion to the subjacent rock, 

 and pushing before it the mass of the glacier till the water has 

 discharged itself by means of the numerous outlets thus formed, 

 when the glacier again retracts and withdraws nearly to its 

 accustomed limits. 



The above phenomenon, which in Switzerland is in general 

 little more than an object of philosophical curiosity, is in Iceland, 

 especially on the southern coast, the occasion at all times of 



freat inconvenience, and occasionally of horrible devastation, 

 he cause of this is in part the enormous accumulation of snow 

 and ice which takes place during the winter in these high lati- 

 tudes, but principally the circumstance that the mountains on 

 which these glaciers rest are volcanoes. Hence, even in quiet 

 years, the melting of the ice is much more rapid in some parts 

 than in others, and this melting begins from the bottom of the 

 superincumbent mass of ice, which, being thus undermined, sub- 

 sides with a loud crash, sending forth long cracks in every direc-. 

 tion, and pouring out torrents of water, the impetuosity of which 

 bears down huge stones and blocks of ice into the rivers, thus 

 stopping for a time, or rendering excessively dangerous all pas- 

 " sage at the fords. In the mean time masses of the glacier, some 

 miles in extent, begin to move forward into the plain, pushing 

 before them rocks of considerable magnitude ; and in the course 

 of a few months will advance half a mile or more, after whic^ 



