ON THE THEORIES OP ELEVATION AND EARTHQUAKES. 63 
To account for this law, let fig. 2 represent a vertical section of an ele¬ 
vated district, perpendicular to the direction of the longitudinal fissures, at 
the instant the formation of those fissures is completed, and previous to any 
relative displacement by further elevation. The planes of the fissures will 
Fig. 2. 
^lilomfeexactIyvertieal,aud would generally moot if sufficiently produced. 
Ihey will consequently divide the mass into complete or tnincateil wedges. 
Under these circumstances it is evident that the subjacent fluid, by the intu¬ 
mescence of which the elevation is supposed to be effected, will exert a 
pressure on the wedge-like portions whose broadest end is downwards, 
greater in proportion to their mass, than on those wliose narrowest end is 
ownwards, while no direct pressure of the fluid may act at all on those 
po ions which form complete wedges. Consequently the continued action 
0 le elevating force will produce a relative elevation of those portions of 
e mass which present the broader surfaces to the fluid pressure, and the 
10 e will immediately assume the form represented in fig. 3. These rela- 
Fig. 8. 
be ehewTi levelling of the surface by denudation, will 
dbe orimnaii,.'^ '^lativc positions of different portions of a stratified bed 
It will be obifr 1^“^ broken by the faults os in fig. 3. 
broken linp n A r n positions of the diffcreJit pordons of the 
26 above enunciated. 
‘nannur In —-'Fhe preceding case afford* an instance of the 
dneed wlthn.ti * ^ horuoutal pressure of great intensity might be pro- 
fi«ul elevation. After the formSion of the 
ProdupJd iJ».;!? of iJ,e elastic vapour, which is assumed to have 
escaoe anri iK* of the* subjacent fluid, would almost necessarily 
P«> and thus destroy in a greater or less degree the fluid pressure be- 
