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ME. EOBEET MALLET ON VOLCANIC ENEEGY. 
8. That there now exist in the interior of the earth large masses of uncombinecl 
metals of great specific gravity and high, fusing-point, and strongly electronegative in 
the chemical scale, as gold and platinum, to which we may add iron if its vapour 
existed in large excess in the original nebula , is highly probable, both on such specu- 
lations as we can so far form as to the order of the play of chemical forces during 
the globe’s formation by condensation, and as perhaps the only way in which the earth’s 
mean density can be reconciled with that of its known superficial crust. 
But the chemical elements composing that crust are on the whole in a state of com- 
bination ; and hence no chemical energy remains stored up for conversion either into 
heat or into work. 
9. For we may obviously, in relation to vulcanicity, pass by those minute chemical 
changes at present going on within the crust, mainly through the action of air and water 
and matter dissolved therein on some of its various constituents. We may even omit as 
insufficient whatever of chemical action took place during the period (probably yet not 
quite ended) when the mineral lodes or veins were formed. In a word, the chemical 
elements of the crust and interior of our globe, so far as we know any thing about them, 
have long assumed a state of chemical equilibrium, and one generally of the most stable 
character. So that we are compelled to conclude that whatever evidences of chemical 
decomposition or combination may be presented to us by the ejecta of volcanoes, the 
chemical action has been brought about by elevation of temperature at the seat of action 
deep below. 
10. That thermal energy has been in part transformed into chemical work and not 
chemical energy into heat. There is therefore no room longer for any “ chemical theory ” 
of volcanoes ; and we are reduced to that commonly, though not quite accurately, called 
the mechanical one. This has passed current at different times in several forms, but 
all resting upon the assumption that our planet now and for long past consists of a 
liquid nucleus of fused matter at a very high temperature, covered by a solidified crust 
of matter chemically much the same, but the materials of the uppermost strata of which 
at least have been dislocated, broken up, redeposited, and variously arranged into surface 
formations by the long-continued action of those superficial agencies with which the 
geologist deals. 
1] . The hypothesis of the existence of a liquid nucleus intensely hot rests mainly upon 
two grounds : — 1st, the nebular origin of our globe in common with all others, as suggested 
by Laplace, by which the interior of a cooling globe must be hotter than the exterior; 
2nd, the observation of temperature, which proves to increase with the depth, though in 
a very discordant sort of way. 
12. That our globe is hotter within than on or near its surface is a fact , but that it 
possesses a liquid nucleus in a state of fusion is only an hypothesis, though a very 
probable one. The rate of increment of temperature with depth, far too hastily assumed 
to follow everywhere one simple arithmetic law, and the facts of terrestrial conductivity, 
so far as these are known, induced the belief that the solid crust is comparatively thin. 
