ON THE THEORIES OF ELEVATION AND EARTHQUAKES. 7l 
ment should result from a great number of small movements is extremely 
small compared with that of its resulting from a small number of greater 
movements. 
It must, I think, be allowed that these considerations furnish powerful 
evidence in favour of the theory which regards those existing elevations 
which have been accompanied by great angular displacements of the elevated 
beds, as the results of movements, some at least of which must havo been 
of great niagnitudc. It should also bo observed that the iiuiuber of up¬ 
heavals of this kind, in the same district, may have been much greater than 
the easting elevation of the district may seem to imply ; for each of these 
ujibeavaU might be, and according to Uie previous reasoning, almost neces¬ 
sarily would be accompanied by subsidences of correspoiuling magnitude, 
and existing elevations can only be the result of tlic upheavals combined 
with the accompanying subsidences. 
Throughout this theory it U assumed, that though the elevating force may 
have acted with variublo intciipity, or may have encountered a variable re- 
sislaaceat dilfereut points of an elevated area at the some instant, such vari¬ 
ations have not been generally rapid and irregular. If however we adopt 
any oilier hypothesis, it may be doubted whether we can diminisli tlie diffi¬ 
culty of conceiving how any great angular displacement can have been given 
throughout extensive areas, to masses .so thick as those which have un¬ 
doubtedly in many instance* been elevated, without supposing such displace¬ 
ment to Lave been accompanied by great instantaneous upheaval. It should 
also be recollected that even if this particular kind of displacement could 
be accomitfed for more easily by means of the hypothesis of niiy irregular 
action of the elevating force, the hypothesis would be iiiaiiinissibla in all 
those cases in which the general phrenomena of elevation should approximate 
to detfinniDate geometrical laws. Instances may exist in which the ph®- 
nomcna present no such approximation, but such can scarcely be considered 
objects of theoretical investigation. The tlicory we have been comiidering 
professes to ofier an e.xplamUion of the various phaenomemi of elevation, so 
far, aad of course so far only, aa they may be characterized by distinct ap¬ 
proximations to certain geometrical laws, by referring the pbtetiomcna to a 
simple and general cause—an elevating force acting as already described 
with a certain appi'oximation to uniformity of iutunaity, but modified by 
particular conditions of ihu clevak;d mass, and by accidental causes called 
*nto action during the resulting movements. It is ouly so fur as this or any 
other theory may accomplish this object, that any real value can attaoh to 
It as a physical theory. 
§ Shxo Ulocments of Elevation and Depressiont and their Helations to 
Paroxymal Movements. 
32. According to the procediug views, the forces which have elevated 
and dislocated the earth’s crust have originated in the. elastic vapours gene¬ 
rated in a subjacent fluid luas.*, in the manner in which such vajMiurs are 
known to be generated in existing volcanos. The analogy seems to justify 
the conclusion that it would be principally by loJig accuinululion that the 
Confined vapours would acquire sufficient elastic force to elevate the super- 
Wcumhont mass, though we arc not sufficiently acquainted with the mode 
m which they are generated, and the conditions which may iufliiciice the pro¬ 
cess, to assert that they might not in certain cases be generated with much 
gr^er rapidity than under the more ordinary conditions Ui which the ele- 
'■■atmg fluid waa formerly, or the existing fluid masses of volcanos are actually 
subjected. Admitting however the gradual accumulation of elevating power, 
