Mountain Building.—Reade. 239 
postulates granted, capable of doing an immense amount of work. 
The conception is now pretty generally recognized as founded on 
a fallacy, for the nucleus of the spheroid is not cooling, but only 
the outer rind to a very small depth while the shell itself is cireum- 
ferentially contracting, except at the actual surface. The result 
*being,as [was the first to point out, that a much less thickness of 
the crust than was generally supposed isin compression. All this 
is matter of recent scientific historyt but for the further elucida- 
tion of. the position I have taken up in my ‘“‘Origin of Mountain 
Ranges,’ I purpose showing that the secular contraction principle 
will only act as a mountain building agent—granting all the im- 
possible postulates required for it—by an expenditure of heat 
and therefore initial energy out of all proportion to the work 
to be done. 
In order to illustrate my meaning and to get the conception 
well into the minds of my readers, I will assume a hard crust 
forming a shell 20 miles thick of equal temperature throughout, 
resting upon a heated nucleus such as we suppose obtains at pres- 
ent in our globe. Assume that this nucleus, cooling only on the 
outer surface to a depth of a few hundred miles, loses sufficient 
heat without in any way changing the temperature of the enclos- 
ing shell, to produce a contraction of 550 feet of a radial bar cut 
out of the nucleus, then in consequence of the principle of cubical 
contraction the radius of the earth would be reduced by three 
times this amount or 550% 3—1650 feet. The hard shell un- 
changed in dimensions would have to fit itself to the reduced nu- 
cleus either by thickening or by corrugation. Let us assume the 
adjustment takes place by corrugation, then we shall have 
1650 6.28 or 10,362 feet of surplus circumference to dispose of 
in folds measured in any direction over a great circle of the globe. 
I have chosen the figure 550 for the purpose of easy compari- 
son because that is the amount of linear vertical expansion that 
would take place in a crust 20 miles thick as assumed in our ex- 
ampleZ raised 1000° Fahr. and is therefore an equivalent amount 
*Origin of Mountain Ranges, Chap. x1. 
+See Smithsonian Report. Record of Science for 1887 and 1888. 
McGee p. 240. 
{This is not obvious at first sight, but it arises from the circumferen- 
tial stretching of the cooling outer layer over the uncooled portion of 
the nucleus. 
$2.75 feet per mile per 100° Fahr. 
