CENTURY OF IOWA GEOLOGY 437 



no place. Relation of land and sea is made causal and essential ; 

 whereas it is only accidental and trivial. The outstanding feature is 

 a broad basin with high mountainous rim, and low sea-level interior. 

 Recent experimental reproductions of those broad basinal tracts 

 which correspond to the oceanic depressions of the geoid are ac- 

 companied by resu4ts having curious significance. They point to 

 the fact that we shall have to modify our fundamental conception? 

 concerning all the major deformations of the earth's crust. 



Instead of distinguishing between continental elevations and 

 oceanic depressions the proper discrimination to be made is between 

 the cordilleran ridges of the continental borders and the intervening 

 lowlands whether above the level of the waters in the continental 

 interior, or below sea-level in the existing oceanic areas. The meri- 

 dional disposition of the continents then comes to be readjusted as 

 relatively narrow orographic ridges in place of broad basin-shaped 

 plateaus. ^^ 



OROGRAPHIC DEFORMATION THROUGH DIMINISHING RATE OF 

 EARTH'S ROTATION 



From the results of recent curious experiments in geotectonics 

 conducted within our boundaries it is inferred that the larger relief 

 features of our globe are not really the complex dynamical phenom- 

 ena commonly fancied but that they are all merely somewhat dif- 

 ferent expressions of the same simple tangential force and direct 

 resultant of the earth's rotation. 



Inquiry into the immediate origin of the great earth wrinkles is 

 usually approached from an astronomical angle. Since on the as- 

 sumption of a cooling globe the contractional hypothesis takes 

 form it is premised that the earth passes through much the same 

 course as does a shriveling apple. 



As is well known, a rotating spheroid possessing notable elasticity 

 does not have the geometric radius coincident with the radial line of 

 molar equilibrium, or repose from stress. The first is a straight 

 line ; the second a section of a parabolic curve the focal coefficient 

 of which varies with the rate of revolution. For obvious reasons 

 the spheroid of the laboratory acts as a homogeneous body. Ex- 

 tending these physical principles to the earth complications at once 

 set in. The zones of rock-flow and rock-fracture necessarily behave 

 differently. The former acts as a homeogeneous body under hydro- 

 static pressure. The latter develops the characteristics of a hetero- 

 geneous body: it flexes, faults, and shears; and gives rise to all of 



"Science, N. S., Vol. L, p. 413, 1919. 



