88 PEOCEEDIXGS OF THE BALTIMORE MEETIXG 



pressions of the same simple tangential force and direct resultants of the 

 earth's rotation. 



Inquiry into the immediate origin of the great earth-wrinkles is usually ap- 

 proached from the astronomical angle. Since, on the assumption of a cooling 

 globe, the contractional hypothesis takes form, it is commonlj- premised that 

 the earth passes through much the same course as does a shriveling apple. 

 Beginning with Descartes, three hundi-ed years ago, and ending today with 

 Suess, the contractional theory finds many adherents. Challenges are few and 

 far between, but important, for they seem to show that the hypothesis has to 

 be critically examined anew, in the light of the more modern advancements of 

 the earth sciences. 



As is well known, in a rotating spheroid possessing notable elasticity the 

 geometric radius is not 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 coefiicient of which varies with the rate of revolution. 

 For obvious reasons, the spheroid of the laboratory acts as a homogeneous 

 body. Extending these physical principles to the earth, complications at once 

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

 ently. The former acts as a homogeneous mass under hydrostatic pressure. 

 The latter develops the characteristics of a heterogeneous body ; it flexes, faults, 

 and shears, and gives rise to all of those tectonic phenomena which are com- 

 monly accounted for on the hypothesis of a contracting nucleus. Tangential 

 compression thus may be initiated without regard to a cooling globe. 



Working with curved prisms, like sectors of the earth, with bands corre- 

 sponding to gravitational control, and under conditions under which there is 

 gradual release of rotational stress analogous to retardation of the earth's 

 revolution, experiments lately performed reproduce to a nicety all of those 

 larger structural features of the earth, such as the ocean basins, the continen- 

 tal arches, Cordilleran corrugations, and orographic foldings. The effects of 

 tangential compressive force which many mountain structures display thus 

 appear to be not the result of earth contraction, but of stress release due to 

 retardation of the earth's rotation. 



Finally, on this new basis, with the force and rate of retardation and the 

 amount of crustal shortening capable of exact expression by mathematical 

 equation, a ready means is provided for realizing not only something of Eli^ 

 de Beaumont's fantastic dream of orographic symmetry, but for gauging in 

 units of human time the age of every mountain uplift, for determining very 

 accurately in like terms the periodicity of every diastrophic movement, and 

 for evaluating in years the span of every era, period, epoch, and stage of the 

 stratigraphic records since life appeared on our globe. 

 « 



Eead by title in the absence of the author. 



LATE 2IISSISSIPPIAX OROGEXIC M0VEMEXT8 IX XORTH AMERICA 

 BY FKAXCIS M. VAX TUYL AXD RAYMOND C. MOORE 



i Abstract) 



Recent stratigraphic studies have disclosed that the Ouachita disturbance of 

 late Mississippian time affected a much larger area in North America than was 



