PRESIDENTS ADDRESS—SECTION C. 89 
of 50,000 feet, then the base of the new deposits will be gradually 
warmed, by conduction of heat from below, to about 1000° F. 
The temperature of the deposits would gradually diminish 
upwards until it was zero at the new surface. Below the new 
deposits the increase of temperature of the old surface would also 
be 1000° F., and the increase for each layer downwards would 
gradually diminish to nothing. Consequently, the level of fusion 
would rise in the old crust nearly 50,000 feet, and the solid crust 
would maintain, approximately, its old thickness. The expansion 
caused by the heat, and, consequently, the internal stresses, would 
be greatest in the old crust, while in the new deposits it would 
diminish upwards to nothing. It is usually supposed that the heat 
would expand all rocks except clay, which at first contracts as part 
of the water is driven off; but it does not seem certain that such 
would actually be the case with deeply buried rocks. It seems 
quite possible that the expansion, which is not much more than 
one inch in two and a half chains for every 100° F., may be well 
within the limits of elasticity of the rocks, in which case 
extension need not necessarily oceur. If, however, the heat be 
sufficiently great to produce crystallisation, then the previously 
non-crystalline rocks would probably become denser and contract, 
and thus cause the surface to sink. This is the opinion of Dr. 
Sterry Hunt, Professor Le Conte, Professor Lloyd Morgan, and 
others ; consequently, it is far from certain that the rise of the 
isogeotherms would produce elevation at all. Professor Le Conte 
has suggested that the increasing heat in the newly laid down 
rocks may give rise to chemical action, which would still more 
increase the temperature ; but Dr. Sterry Hunt thinks that any 
chemical processes which might be set up in the buried sediments 
would absorb rather than generate heat. 
Mr. Mellard Reade, who is the ablest exponent of this 
theory, claims that an expansion would certainly take place quite 
sufficient to account for mountain ranges. In his “Origin of 
Mountain Ranges,” 1886, he says that if an area of 500 miles 
long by 500 broad has its temperature raised by a mean of 1000° 
F., the result would be an expansion of 52,135 cubic miles. 
Now, this heating implies the deposition of more than 50,000 
feet of sediment over the whole area, and does not take into 
consideration any thinning out of the deposits towards the margin. 
Either we must double the area of deposition or halve the effects 
of expansion. Taking the latter as the more probable, we find 
that the expansion would be sufficient to form a mountain range 
500 miles long, 15,000 feet high, and about 28 miles broad at the 
base, which is not a high nor a broad range for such exceptionally 
heavy sedimentation ; and even this allows nothing for condensa- 
tion produced by a temperature certainly sufficient to induce 
crystallisation, nor for condensation produced by pressure, nor 
for denudation during elevation, which would reduce the height 
