438 IOWA ACADEMY OF SCIENCE Vol. XXVI, 1919 



those tectonic phenomena which are commonly accounted for on 

 the hypothesis of a contracting nucleus. Tangential compression 

 thus may be initiated without regard to a cooling globe. 



In laboratory experimentation on curved prisms, with bands cor- 

 responding to gravitational control, and with conditions under 

 which there is gradual release of rotational stress analogous to re- 

 tardation of the earth's rotation, there is reproduced to a nicety all 

 of those larger structural features of the earth such as the ocean 

 basins, the continental arches, cordilleran corrugations, and oro- 

 graphic foldings. The efifects of tangential creeping which many 

 mountain structures display thus appear to be not necessarily the 

 result of earth's contraction but of direct cumulative stress-release 

 due to secular retardation of the earth's rotation. 



The bearings are far reaching. On this new basis, with the force 

 and rate of retardation, and the amount of crustal shortening cap- 

 able of exact expression by mathematical equations a ready means 

 is provided for realizing not only something of Elie de Beaumont's 

 fantastic dream of orographic symmetry, but for gauging in units 

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

 within very narrow limits in like terms the periodicity of every 

 diastrophic movement, and for evaluating in years not only the 

 span of every era and period, epoch and stage of the stratigraphic 

 record since life appeared on our globe, but stratigraphic chronology 

 long antedatii\g the life record.^® 



GEOLOGICAL SURVEY OF IOWA 



The collection of data concerning the mineral features of our 

 state has now been carried on systematically and without interrup- 

 tion for more than twenty-five years. These have been years of 

 exceeding productivity. Along with the more strictly scientific 

 phases have gone on hand in hand an exhaustive investigation of 

 our mineral resources. Thirty sumptuous volumes amply attest 

 the vigor with which the work has been prosecuted. Many dififerent 

 worlcers have been engaged upon the myriad of problems presented. 

 Varied as the results have been it has been surpassed by novelty. 



Monumental inc_[uiry of this kind is, of course, necessarily com- 

 posite in character. The investigations are conducted by all earth 

 students of the state, reinforced at times by chemists, physicists and 

 engineers, and even by zoologists and botanists. Altogether the 

 combined efiforts make a most creditable showing. No other state 



2'Bun. Geol. Soo. Amerio.-i, Vol. XXX, 1919. 



