CAUSES OF THE ELEVATION OF THE STRATA. 95 
whilst they elevate another, the modus operandi by which they ac- 
complish this is equally obscure. 
4. Abandoning the idea that the dislocated and tilted condi- 
tion of the strata is the result of chemical agencies, some philoso- 
phers have turned their attention to the gradual refrigeration of 
the globe, as the great cause of geological changes ; but still with 
discordant, views respecting the manner in which it would ope- 
rate. A ball consisting of an exterior solid crust, and an interior 
liquid mass, is floating in a medium whose temperature is less el- 
evated than its own : What law will the cooling observe as it 
proceeds ? Will it be most rapid, and the contraction most con- 
siderable, in the crust, or in the fluid it contains ? 
5. M. Elie de Beaumont supposes, that it will be greatest in 
the latter, and that the crust becoming too large for the body it 
is required to cover, will collapse, and accommodate itself to the 
diminished magnitude of the internal nucleus, rising into ridges 
along certain lines that are not very remote from each other ; 
and that it is in this way that the strata have been shifted from 
theiroriginal positions, and mountain ranges formed. M. Cordier, 
on the other hand, represents that the cooling and contraction 
will be the greatest in the crust. Fissures must therefore be created, 
in some places, to which it may be expected that the superabun- 
dant matter will be directed by the pressure of that part of the 
crust in which the cohesive force is not yet overcome. This 
must produce a bulging out of the surface along the line of the 
fissures; a ridge of granite, with the transition and secondary strata 
adhering to it, and reposing upon it in an inclined position, on 
each side. This hypothesis agrees better with the facts there- 
fore than the other. 
Whether we shall ever arrive at accurate knowledge, and con- 
clusions in which we may repose undoubting confidence, respect- 
ing the primary causes of geological phenomena, is perhaps doubt- 
ful. The minds of the philosophers who are engaged in the cul- 
tivation of this science, are now directed with intense interest to 
this particular subject, and it may be hoped that correct results 
will be obtained. But even if they should not, the value of the 
knowledge we already possess, will not be much the less on that 
account. Until within a very few years, it was the commonly 
received and accredited doctrine, that light consists of minute 
particles, thrown off with immense velocity, from the luminous 
body. At present, the opinion that the phenomena of light are 
the effect of undulations produced in an elastic medium dispersed 
through the universe, threatens to supplant the other. But 
whether we embrace one or the other hypothesis, all the great 
principles and doctrines of the science of optics will remain un- 
affected, and with no diminution of their truth and certainty. 
And so will it be with regard to the cardinal facts and doctrines of 
geology, whatever the uncertainty under which we labor in re- 
gard to the primary causes of geological changes. 
