88 PRESIDENT’S ADDRESS—SECTION C. 
He says, “surfaces of equal temperature within the crust must 
be continually changing their form and exposing thick beds near 
the exterior to alternations of temperature. The expansion and 
contraction of these strata will probably form rents, raise moun- 
tain chains, and elevate even continents.” The letter is very 
vague, but he evidently saw the impossibility of land being 
elevated above the sea by this cause, unless the rise of the 
isogeotherms was less rapid than sedimentation ; for he says, 
“The whole expansion, however, may not take place until ong 
after the filling up of the sea,” but he gives no reasons for this 
opinion. 
Sir J. Herschel, who thought of this theory independently of 
Babbage, and enunciated it at the same time as his theory of 
alteration in pressure, applies it to the elevation of continents 
and to the formation of volcanoes, but says nothing about moun- 
tain ranges. However, he states the theory very clearly. He 
says: ‘ With equilibrium of temperature and pressure within the 
earth, the interior isothermal strata will be spherical, but as they 
approach the surface they will conform themselves to the configu- 
ration of the solid portion. But when the concave bottom of 
an ocean is filled by deposition it may become horizontal, or even 
convex, and the isotherms will rise upwards. But if the deeper 
strata be already at the melting point, its level will be raised, 
and the new strata, water included, will be melted.” Lyell misin- 
terpreted Babbage’s meaning, which is not very clear, and took 
the expansion to be upwards only, in which case it appears to be 
miserably inadequate to perform the work assigned to it ; but in 
the anniversary address to the Geological Society of London, in 
1859, Professor Phillips, speaking about the theory, said: “ If 
we suppose a change of temperature of 100° F. to cause expansion 
in a solid mass 500 miles across, this would occasion a change of 
linear dimensions of above a quarter of a mile in limestone and 
sandstone. If the pressure occasioned by this were relieved by 
one vertical fault it must be 16 miles in height, if by one general 
curve upwards it would have an elevation in the middle of about 
8 miles. Though, in fact, neither of these assumptions as to the 
form of the surface of relief can be adopted, they show how great 
is the Jower of changing form and relative height generated by 
changing temperature in rock masses.” In the same year 
Professor James Hall pointed out that, as a matter of fact, 
mountains had been formed only in areas of great sedimentation, 
but although this evidence added immensely to the probability 
of the theory, it nearly died out, until it was independently 
supported in 1886 by M. Faye and Mr. Mellard Reade. 
T will ask you to allow me to explain a little more precisely 
what is supposed to take place in these thick sediments. If we 
suppose the bottom of the sea to be at a temperature of zero, and 
to be gradually covered up by deposits which attain a thickness 
