354 Transactions.— Geology. 
tend to lengthen. As before stated, the tides have this effect, the velocity 
is lessening, the polar axis is therefore lengthening, thus subjecting the 
erust to a continually increasing tensile strain under which it eventually 
yields. 
That it does yield is proved by the known fact that the earth has now 
the form due to its present rate of rotation. This cannot be a mere coinci- 
dence, but must indicate that the crust has yielded to the strains which 
tend to lengthen the polar axis, and we may take for granted that it will 
continue to do so. These are tensile strains and the fracture must therefore 
be sudden and complete. If they had been compressive, no actual fracture 
would take place, for the molecules would simply arrange themselves closer 
together and change of form would follow without fracture. With tensile 
strains this is impossible for, with them, the molecules are forced further 
and and further apart becoming every day less able than before to resist 
the strain, until at last the distance between them becomes greater than 
that over which the attraction of cohesion can act, when sudden fracture 
takes place. 
As soon as the crust yielded, the fluid interior to the earth, no longer 
held back by it, would at once take the form of equilibrium; that is, it 
would rush towards the poles, leaving the equatorial part of the crust un- 
supported ; the latter would be unable to bear for a moment its own weight, 
or even a ten thousandth part of it; it would break at once at the weakest 
parts. The primary lines of fracture would tend to be north and south, but 
as a curved surface like the earth’s crust cannot fit itself to a different 
curve, fractures transverse to the first would be necessary to allow even such 
an approximation as would enable the strength of the material to bridge 
over the minor inequalities. There will, therefore, be east and west as 
well as north and south fractures. 
Each line of fracture would become a line of volcanic action. 
A Let Fig. 1 represent a section of the earth at 
the equator after fracture. The central part is 
of less diameter than it was before, part of it 
having gone towards the poles. The crust is 
therefore too large to fit on to it, and cannot 
fall in so as to be supported by the central part 
without shortening by compression. We will assume that all the crust 
except the two masses at A has compressed and fallen in. It is apparent 
that before they can do so also, they must crush together lengthwise, as 
they have to occupy a smaller space than before, 
Wherever matter is compressed heat is evolved, and this will happen at 
A. It is to the heat thus evolved that I attribute the elevation of a moun- 
