262 Natural History of Volcanos and Earthquakes. 
the falling in of its cone at one period, appears to be balanced 
by the accumulation of ashes at another. 
If arent, reaching from the surface to the melted matters in 
the interior, be of great length, but not open throughout its 
whole extent, the first eruption will take place where there is 
the least resistance. 
If this channel become obstructed, the volcanic fire will seek 
another vent.* Violent concussions may open new fissures} and 
close old ones, by which frequent changes may be produced in 
the channels of the lava and water. - Fissures obstructed by lava 
are closed so firmly as to be incapable of being re-opened ; new 
ones, therefore, are formed. Thus it is, at least, if a volcano 
produce eruptions from its sides. If it happen that a wide and 
lasting vent be formed, all partial workings in the neighborhood 
will cease. A similar combination, although on a somewhat 
limited scale, is presented by groups of mineral springs, espe 
cially of hot springs. In such groups, new channels are seen to 
open, new springs to rise, and old ones to close. ‘The only dif- 
ference is, that, as these changes are not accompanied with any 
violent action, as is the case with volcanos, they require a greater _ 
length of time for their accomplishment. 
We have, in the preceding inquiries, as yet only supposed the 
admission of water from the sea. But this does not seem always 
to be the case, even in volcanos situated near the sea. Acco? 
ing to Hamilton,{ the water of the springs and wells of Torr 
del Greco diminished so much a few days before the great erup 
tion of Vesuvius, on the 15th June, 1794, that the corn mills at 
the principal spring were nearly stopped, and it was daily nece™ 
sary to lengthen the ropes in the wells, in order to reach the 
water. Some wells dried quite up, and on the morning of the 
12th June, at Resina, a subterranean rumbling noise was he 
after a heavy rain. Monticelli and Covellig relate that, before 
een ae 
* Thus the interior of the crater of the Peak of Teneriffe, shows it to be a vole 
cano, which for thousands of years has thrown out fire only from its sides- 
Humboldt, Reise, t. i. p. 195. staal 
f According to the inhabitants of New Andalusia, the soil in various districts 
their province has become more and more arid, in consequence of the frequent 
earthquakes with which they are visited from time to time —V. umboldt, Reis 
hp. 2. t Phil. Trans. for 1795, p. 79. fi 
g Loco cit. pp. 12 and 63. See also Monticelli, in Leonard's Taschenbuch 
die gesammte Mineralogie, vol. xiv, p. 87. 
