ON THE THEORIES OF ELEVATION AND EARTHQUAKES. 57 
fissnmed conditions. It has been one principal object of this part of my Ro- 
p<\rt to indicate distinctly as I have proceeded what those conditions are, and 
the nature of the experiments by which we may hope to test their admissi¬ 
bility. It is only by a mode of investigation in which the introduction of 
error is to be sought in the assumed conditions, and not in the general rea¬ 
soning by which we deduce our results, that we can hope to arrive at any 
real approximatiou to demonstrative truth. 
Part II.— On the Effects of Subterranean Forces on the Solid Crust of the 
Earth. 
Section I. Theories of Elevatioji, 
The theory of elevation which I shall now proceed to explain may be 
^gardf-d as independent of the speculative views which have been developed 
in the first Part of tliis Report, if we commence with certain hypotheses re¬ 
specting the constitution of the superficial portion of the earth s mass. With 
this view of the subject, the fundamental liypotlicsis would be, that portions 
of the solid crust of the cartli, which, in some cases, were of large horizontal 
dimension*, had reposed, at some past ejiochs, ou fluid matter capable of 
exerting an expansive force on tlic superincumbent solid masses sufficient to 
elevate and dislocate them. The superficial boundaries of each particular 
area which lias tlius been elevated, are supposed to have been determined 
either by the greater thickness and consequent stability of the crust beyond 
the limits of the disturbed district; or by the boutidaric*:* nf the fluid masses 
themselves, supposing them to have existed as internal lakes without free 
mtercommunication through a general fluid nucleus, or by other means. It 
is immaterial to this theory how tin's state uf tJic globe may have been pro¬ 
duced, whether it was a primitive state or one derived from an anterior state 
by the operation of natural causes. It is desirable I think, in the actual 
slate of geological kuowledge, to place the theory in ibis distinct and inde¬ 
pendent point of view. At the same lime we should dejirive the science of 
some of its most interesting speculations, if we were to assume the non-exist¬ 
ence of physical causes active in producing physici;! phenomena, at epochs 
planT*^ which we are here commencing in the history of our 
§ PrimaTif Pheenomma of Elevation, 
, Tension of the Elevated Mass, —It is not essential to this 
eory thatwe should suppose the subjacent fluid to have been confined to 
y is only necessary that portions of the crust around the con- 
nes 0 the disturbed district should havo been sufficiently Ann to resist the 
e cci of the elevating forces which dislocated the thinner and weaker part 
o e crust within the boundaries of the elevation. The condition however 
may jier aps be more distinctly conceived if we suppose the fluid mass to 
lave been eoutained in deM;rra*inate and separate cavities, though it might 
e equa y well 8alii.fied by the state of the internal surface of the solid crust 
flesenbed in articles 16 and 17, previous to the completion of a distinct 
cavity by tJie formation of solid floors. 
oupposiDg the subjacent fluid to expand by the generation of elastic 
vapour, the portion ol the crust witliin the boundaries thus defined, would 
e acted on by the expansive force of the fluid, producing a hydrostatic 
prcMure, which would be approximately equal at every point of the lower 
ur ace of the solid mass elevated by it, supposing the elastic force of the 
urn to increase by the continuous and not by the sudden and instantaneous 
