38 
REPORT—1847* 
only evidence on which the troth of our primary awump mns can M 
some persona have appeared to think that the hypothesis of the ojmd 
solidity of the earth is in itself so far prelenible, that any other hvpothejii 
required, as it were, a justification. In the preceding bnef remarks 1 hat 
wished to show that, instead of such being the ease, the hypothesn. of the 
former fluidity of the earth is, with reference to physical theories, more simple 
than that of its primitive solidity. But whatever hypothesis we adopt, we 
must ever recollect that the final tost of its tnilh must nlwavs be wught id 
the process of an accurate deduction of consequences resii ting from ow 
original assumptions, and a careful comparison of such calculated results 
with observed phtenomena. In no science perhaps is it so ewutial as m 
geology to bear in mind this great single rule of inductive philosophy, 
cause in no other science is there the same temptation to violate h. t a 
alone in the general accordance and harmony' ol’ our theoretical dMuctioo* 
with the results of observation that we must seek the ultimate evidenre o 
the truth of our theories. . 
I shall first proceed to make a few' remarks on the theory founded on tM 
second of the hypotheses above mentioned. It is commonly called the 
chemical theori/ of volcanos. , 
8. Chemical Theory of I'vlcaHos .—In this theory, as I have already 
the fundamental hypothesis is that the interior of the earth, at the depth of 
perhaps three or four miles, consists of an unoxidized solid tnasf*. It i* sup* 
posed that this maws is accessible to ivater and atmospheric air, by the decom¬ 
position of which it becoim-s oxidized, anil that the heat generated in thu 
chemical process is snflieient in many instances to reduce the mass in whien 
it takes place to a state of fusion. Hence the existence of volcanos. 
With regard to the efliciency of the chcniicul causos assigned by this theory, 
difterent opinions have been entertained. When first promulgated by Davy 
it was opposed by (Jay-I.ussac*; more recimtly it has been 8n|)ported b)' 
Dr. Daubenyt, and ojipiised by M.Bischoff J:. Between such high authon- 
ties I have no pretension to decide; but tlie theory appears to me to involve 
a mechanical difficulty of the gravest character. It was first iuiliwtpd by 
Gay-Imssac, and has never in my opinion been explained away, h consuls 
in the supposed admission of water and air to the lower regions of the 
volcanic niass. It is huppoKcd that fissures exist by which a cotniBunication 
is established between the water of the ocean and roimc lower portion oflh« 
fluid lava; but it was suggested by the distinguished chemist last mentioned, 
that if water could desceml freely down theso fissures, there was no rci'on 
why the fluid matter with which the fissures by hypothesis coinnmn'cal*® 
below, should not ascend through them, i>rovided the hydrostatic pressure at 
the bottom of the fissure was greater than the weight of the descending 
column of water. And if the fissures aflbrd a free comumuicaiioii, this must 
necessanlj- be the case, unless the vertical height of the column of water, 
measured from its lowest point to the level of the surface of the ocean, be m 
the proportion of about <2^ to 1 to that of the vertical Jicight of the fluid l»vi 
above tlie point of junction with the aqueous column, supposing the specifle 
fann^ 1 y^ouUl place the upper s«[* 
ace of the fluid niasa of a volcano not in violent action, at a considerable 
ortTrir t*-«« '^^th respect to any 
the laiger existing volcanos; and we know that it certainly is not true 
* Annales de Chimic, vo]. sxii. p. tl5. 
