246 Prof. Sillimari'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 — rboiling 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 in a 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 is not 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 — tena- 

 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, in 

 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 

 occurring where the force was the greatest and the resistance the 

 least. 



Those who adopt the theory of nebular condensation, and sup- 

 pose the earth to have been formed by accumulation of such ex- 

 panded materials, evolving heat as they became solid, will find 

 no difficulty in admitting also the agency of the causes that have 



