A RSET ee SAREE Gee a Tee 
Se Ee ee eS ae 
Condition of the Earth's Interior —Mountain-Making. 11 
1. That this restriction of the interior liquidity of the earth 
to an undercrust layer, does not require in itself any modifica- 
tion of the views I presented, more than twenty-five years since, 
on the results of the earth’s contraction, since there is still a 
flexible crust and mobile rock beneath it. 
2. The condition of the earth’s interior here recognized is, 
as many readers will have observed, that suggested long ago by 
Professor W. Hopkins—the author who first offered a mathe- 
matical argument in favor of the earth’s either having a very 
thick crust or being solid throughout.* In a paper on Theories 
of Elevation and Karthquakes, in 1847,+ Prof. Hopkins argues 
that the central mass of the earth became solid in consequence 
of the pressure, whenever the temperature within reache 
limit that permitted of it; that crusting at surface from cooling 
commenced afterward; and that between the regions of interior 
and exterior solidification, there long remained a viscous layer, 
which, in the progress of time, was gradually contracted by the 
union of the solid nucleus to the thickening shell. 
? 
than water, changes to water under pressure, has ‘been appeale 
to in Support of the conclusion. The pressure to which the 
material within the earth is subjected is so great that experiment 
can never imitate it, or directly test its effects. Beneath only 
earth should be as completely free as it is from tidal movements 
In its mass, 
* Trans. Roy. Soc., 1839. ea, 
+ Rep. Brit. Assoc. for 1847, p. 33. The theory of elevation advocated in this 
Paper attributes elevation, not to lateral pressure from contraction, but to evolved 
i On. 
. Vapors un erneath the elevated region. The array of facts which have been 
i z 
resented respecting the positions of mountain ranges, their relations to the great 
* * pa c= peda f 
e 
and ae natural evolution of the whole from the universal action of the one 
be also that mountains so raised could not hold themselves up, has seemed to 
an insuperable difficulty to the success of the method. 
