82 On the Ice Mountain of Hampshire County, Va. 
A still more interesting and striking proof of the perfect isolation 
from external causes, by a poor conducting covering, is attested 
by the fact, that a large glacier of ice and snow was overflowed 
by a stream of hot lava from Mount Etna, without being destroy- 
ed.* The ice thus covered by the lava, was protected by it from 
the summer’s heat, and continues thus preserved to the present 
day. ‘This can only be explained by supposing that the lower 
portion of the lava current, immediately upon its contact with the 
ice, was reduced to the temperature of the glacier, and that this 
reduced stratum, from its imperfect power of conducting heat, 
protected the ice from the hot lava above. Whatever may be the 
explanation of it, or however paradoxical it may appear, the fact 
is attested by too high authorities to be doubted. Public atten- 
tion was first called to this interesting fact in 1828, when the 
discovery was made by Signor Gemmellaro, in searching after 
ice. It has been subsequently examined by Lyell and other dis- 
tinguished geologists, who confirm the report of Signor Gemmel- 
laro. Excavations made for removing the ice, have exposed the 
_ lava for several yards, overlying the glacier, and so superimposed, 
that the relative position of the lava and glacier can only be ac- 
counted for by supposing that the latter was overflowed by the 
former in a melted state. Monte Testaceo may be instanced as 
presenting a phenomenon more strictly parallel with that of the 
Ice Mountain, and as affording a happy illustration of the principle 
so frequently alluded to. Monte Testaceo is situated in one of 
the suburban riom? of Rome. It is merely a large mound, com- 
posed of fragments of earthenware vases and urns, and is supposed 
to mark the site of an extensive ancient pottery. This accumu- 
lation of bad conducting materials preserves a uniform temperature, 
many degrees below the main temperature of Rome, and on this 
account artificial cavities formed by digging in the sides of the 
mound, are used as wine vaults. In July, 1773, Prof. Pictet 
found by observation, the temperature of one of the caves to be 
A4A°, while that of the external atmosphere was 78°.+ If thiscom- 
paratively small accumulation produces so great a depression in 
Rome, where the mean temperature is 60°, it can be readily con- 
ceived that the still greater accumulation at the Ice Mountain, 
** Lyell’s Principles of Geology, London edition, Vol II, p. 124. 
+ Edinburgh Philosophical Journal. 
