52 
OROGENY AND EARTH’S ROTATION 
curved radius of no-strain takes place not because the spheroid is 
becoming smaller through nucular shrinkage but for reason of its 
approach to the globe’s normal geometrical radius. 
In the final analysis of the major relief features of our globe 
the hydrosphere is, for simplicity’s sake, left out of account. The 
effect then is as if the entire face of the earth were a land area. 
A condition is premised analogous to that of our waterless moon. 
Genetically the seas serve only to obscure the tectonic essentials 
of’relief expression. As Prof. Eduard Suess astutely observes 
the secular movements of land elevation are without significance 
in the determination of the grander forms of the earth’s surface. 
To physical causes of universal character must such land forms 
be assigned. 
Since the immediate cause of the great earth wrinkles is usually 
approached from the astronomical side the contractional hypoth¬ 
esis takes form on the assumption of a cooling globe. It is prem¬ 
ised that the earth passes through much the same process as does 
a desiccating apple. For a period of nearly three centuries this 
idea largely prevails. Beginning with Descartes and ending with 
Suess the contractional hypothesis finds many adherents. Chal¬ 
lenges are few, but nevertheless important. They serve mainly 
to show that the hypothesis really has to be examined anew, in the 
light of the more modern advances in geological science. Al¬ 
though the expansion theory of Hutton, the theory of isostasy of 
Dutton, the theory of extensive crust-glide of Reyer, and the 
theory of local crustal upheaval of Rothpletz cannot be expected 
completely to replace the contractional theory they especially serve 
to call attention to certain of its short-comings. There are still 
stronger objections than these to the contractional theory of or¬ 
ographic and continental genesis. These appear as the direct re¬ 
sults of practical experiment in the laboratory. To some of these 
attention is presently directed. 
The idea of regarding the major relief expression of the earth 
as an immediate derivative of a shrinking interior due to secular 
cooling of a once molten globe appears to have originated long, 
long ago with that famous old French philosopher, Rene Des¬ 
cartes ^ who flourished in the early half of the Seventeenth cen¬ 
tury. Essentials of the same view are formally accepted by other 
1 Principia Philosophise, 1644. 
