72 
REPORT—1847. 
it is manifest that its first efl'ect would be a gradual, and possibly a slow and 
long-continued elevation of the superincumbent crust. If this proceeded 
till the crust became dislocated, the process of elevation might then assume 
instantaneously a paroxysmal character, iu consequence of the sudden dimi- 
nutioD of resistance which would result from the dislocation of the msM, 
and independently of any sudden increase of intensity io the elevating force. 
The degree in which this paroxvsinnl character would manifest itself, would 
depend on the completeness and rapidity of the dislocation, and the aniouut 
of resistance in.^tantaneou5ly destroyed iW it. In order that the mass sLouliJ 
be elevated to the point ot dislocation, it would be necessary that the ui). 
ward pressure should exceed the weight of the uplified mass by a force 
(which we may denote by !•') sufficient to overcome that part of the reist- 
ance to the movement w hich depends on the cohesive power of the uiass. 
Ihosewho are accustomed to mechanical investigations of this kind, will 
p ceive la le nearly horizontal tension depending on the coheMonacts 
at a great mechanical diBadvantage in opposition lo the nearly vertical fluid 
probably always be small compared with the 
nP ^ elevated muss. Still it is easily conceivable that F might be 
for “5 ® to produce a great paroxysmal nioveraeut Suppose, 
and to onc-fifticth of the weight of the mass, 
cohr.,i.n ° complete as to destroy all sensible effect of 
H tl>e upward movoiuent. If this force continued to 
aboiTt Vthe mass tlirough 
times as creat- if'fir elevation would be four 
w“re oulf.?M^ti^r ^ «nnutes,mne times as great, and so on. IfF 
Bpondlne^levaHoi« above supposed, the corre- 
o»<^-tlnrd. as gi’cat as tho^e 
of paroxysmal ninv#im recollected, in estimating the probability 
posFtiorwe theoretical considcrationsf that, in thb e/- 
expansive force of tho ' of the po.ssiblo sudden Increase' in the 
tiorsTch instant of paroxysmal 
«olo«g Swccanof?er no^fP’”"‘‘’““ appear to indicate, 
I think we can at present w^tT *^®“’Pj,*''*‘'.®*P'“naLion of such explosions than 
generation of elastPo vajiours aJ afc"J **!?”' ‘ K ^ '“i**®* 
small an excess nf thn u..: i * events., the above examples show how 
sufflcG to produce a paroayuS ele«t“o" ““ 
subsidence immedktdv^^ji.llf ^sumed a paroxysmal character, the 
character, but U ^ extrFn doubtless assume a similar 
Would imraediatelv cease |joprobahlo that the downward movement 
likdy to eoutiuuu^oTubuid? 'll 
thus as great dislocatinc rnovemn?!, penod of lime; and 
gradual elevation, so it is aW. n L ! have been preceded by 
have been generally fol- 
the eievatrng^fluid, as^m-eSrary external to 
citing cause is by hypothesis the ori^n^f ***^«“escejice, since the cx- 
sunied to be due. Still which the fluidity is as- 
U'gleeted; they maybe on tlir» mnt ^comlary causes are not to be 
fions of deiuulation and denoBition ‘^^^'^^'^''"pcrtaDCe. The opera- 
the processes of elevation hmH A exercise an important influence 
‘«a«s of several huudrer or a sedimentary 
c havu been deposited (as such ’^^''cral thousands of feet in thickness, 
P (as such masses have been) over an extensive area. 
