eat “ery 
246 Prof. Silliman’s Address before the 
May we not suppose, that we now understand why the heat of 
the earth regularly increases as we descend, one degree of Fah- 
renheit for every forty five or fifty feet of descent; eighty two 
to eighty three degrees of Fahrenheit having been recently ob- 
tained in a spouting fountain of an Artesian boring at Paris, sunk 
to the depth of more than eighteen hundred feet, or over one 
third of a mile ; the heat of a hot summer’s day is thus obtained, 
unaffected by the atmosphere above, even when at zero. ; 
The conclusion to which this regular progressive increase of 
heat, supposing it to continue, conducts us, is obvious, and is fa- 
miliar to geologists—boiling water at the depth of two miles, ig- 
nited rock at ten miles, melted rocks at one hundred. Who can 
say that it is really so, and who can say that it is not? Are we 
then walking upon a shell—a frozen crust? If this cannot be 
certainly affirmed, neither can it be positively denied ; while the 
actual eruption of molten rock through the ruptured crust of the 
earth, many times ina year, from some of its hundreds of ignivo- 
mous mouths, demonstrates that rocks are indeed melted in ama- 
zing quantities and at profound. depths in the interior ; while 
innumerable thermal and boiling fountains in all parts of the 
world, prove the elevated temperature of the interior. 
It isnot necessary to suppose with Mr. Lyell, that there are in- 
ternal igneous tides of extensive prevalence that by their afflux 
will melt down the crust of the earth; for, from the analogy of 
volcanoes, we may suppose that the interior of the earth, may be 
in general only in an ignited or softened or pasty condition—ten® 
cious but not flowing liquid, like water or melted iron ; except 
that occasional accumulations of heat in particular regions, aris- 
ing from local thermo or galvanic or chemical action might, 12 
those places, impart unusual fluidity; and joined with explo- 
sive power from steam and imprisoned gases, as well as from 
expansion, and (it may be admitted also from local igneous tides) 
the result would or might be a rupture of the crust, and an out 
break or overflow of lava—in a word, a volcano; the explosion 
oecutring where the force was the greatest and the resistance the 
_ Those who adopt the theory of nebular condensation, and stp 
pose the earth to have been formed by accumulation of such eX- 
panded materials, evolving heat as they became solid, will find 
a no difficulty in admitting also the agency of the causes that have 
