190 QUANTITY OF EJECTED MATTER. 



wood. It soon cools externally, and therefore ex- 

 hibits a rough, unequal surface ; but, as it is a bad 

 conductor of heat, the internal mass remains liquid 

 long after the portion exposed to the air has be- 

 come solidified. That of 1822, some days after it 

 had been emitted, raised the thermometer from 59^ 

 to 950 at a distance of 12 feet; 3 feet off, the heat 

 greatly exceeded that of boiling water. The tem- 

 perature at which it continues fluid is considerable 

 enough to melt glass and silver^ and has been found 

 to render a mass of lead fluid in 4 minutes, when 

 the same mass placed on red-hot iron required dou- 

 ble that time to enter into fusion. Even stones 

 have been melted when thrown into the lava of 

 Vesuvius and ^tna.* 



Quantity of ejected Matter. — The greatest amount 

 of volcanic matter ejected at any single eruption 

 occurred in Iceland in 1783. This island, ever since 

 the twelfth century, has been subject to a series of 

 eruptions ; and, during the whole period, there never 

 has been an interval of more than 40, and rarely of 

 more than 20 years, without an eruption or an earth- 

 quake. Some of these have lasted six years with- 

 out ceasing. Earthquakes have often shaken the 

 whole island at once, causing great changes in the 

 interior, such as the sinking down of hills, the rend- 

 ing of mountains, the desertion by rivers of their 

 channels, and the appearance of new lakes. New 

 islands have been thrown up near the coast, some 

 of which stiil exist, while others have disappeared 

 either by subsidence or the action of the waves. 



In June, 1783, the volcano Skaptar Jokulj in Ice- 

 land, commenced throwing out a torrent of lava> 

 which, with slight interruptions, continued to flow 

 for the space of two years, filling up rivers and 

 lakes, overflowing and destroying villages, forming 

 immense fiery cataracts from 12 to 15 miles wide 



* Daubeny on Volcanoes, 



