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 boihng 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 JStna.* 
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 still exist, while others have disappeared 
either by subsidence or the action of the waves. 
In June, 1783, the volcano Skaptar Jo/cul, 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, 
