676 T. C. CHAMBERLIN 
protrusion of the continents, or else both of these combined their 
good offices, as is most probable. There do not seem to be other 
competent alternatives. 
If the rejuvenation really cccurred at intervals, as implied in the 
statements already made, while the denudation of the continents, 
the loading of the borders of the basins, the loss of heat, the internal 
changes and other assigned agencies of deformation have been con- 
tinuous, there must apparently have been some adequate means of 
accumulating the constantly growing stresses until a stress-limit was 
reached and yielding followed. This power of accumulation must 
have been adequate to the deformative results that followed. This 
forces a consideration of internal conditions. 
The critical question that now arises is this: 
Is the earth essentially a plastic body or at most a visco-solid, as 
so long held, or is it essentially an elastico-rigid body? This seems 
to me nearly equivalent to the question: Is the earth essentially a 
fluidal or quasi-fluidal body, or is it essentially a crystalline body ? 
No one questions that it is partly the one and partly the other, but 
which is it dominantly in its working habit? If the main mass of 
the interior is fluidal or quasi-fluidal, the whole may well be viscous 
or plastic in its body habit and yield indefinitely and continuously 
to stresses that tend to deform it. Continuous loading may, in this 
case, be followed by continuous subsidence; continuous unloading, 
by continuous uprising, if hydrostatic equilibrium had been dis- 
turbed. Not so with a typical crystalline mass. The crystalline 
structure has for one of its essential features the definite arrange- 
ment of the molecules of each crystal in determinate positions with 
reference to adjacent molecules. Any stress that tends to move 
them from these determinate positions is resisted by an elastic force- 
Up to the elastic limit a strain only results, not a shear. Deforma- 
tion is thus specifically limited until the elastic yield-point is reached. 
Beyond this the mass may be sheared, granulated, or fragtured. 
When crystals are intimately interlocked, as they are in typical 
holocrystalline rocks, the joint mass partakes of the qualities of the 
interlocked integers. In such a firm inter ocking of elastico-rigid 
units, stress gives rise to strain, but not to continuous shear, up to 
the yield-point of the elastic mass or of some of its integers. Beyond 
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