'212 C. SCHUCHERT THE NORTH AMERICAN GEOSYNCLINES 



(4) The isostatic oscillatory movements in compensation for transfer 

 •of load from one place to another; areas of sedimentation tend to sink, 

 .and eroding ones rise. Isostasy is an important cause of crnstal move- 

 ment, but is of secondary import to those produced by earth shrinkage. 



If we agree with T. C. Chamberlin that the earth since its growth out 

 ■of planetesimals born of the sun has shrunk 570 miles radially, we see 

 here the primal causation for the wonderful cyclic reelevation of the lands 

 :and sinking of the oceans, and much of the consequent periodic changes 

 in climate. 



That the earth, under any theory of earth origin, is a shrinking mass, 

 is shown mainly by the periodic folding of the lithosphere into mountain 

 ranges, and by the subsidence of the oceanic areas. The crustal shorten- 

 ing is further evidenced in the long-continued recurring times of epei- 

 rogenic Avarping movements that culminate in the quicker orogenic ones. 

 This crustal shortening, due to radial shrinking, follows upon the loss of 

 interior heat, magmatic alteration, and extrusion of lavas, ashes, water, 

 and gases, and mainly through molecular rearrangement of the centro- 

 sj)here engendered by the continuous attraction pressure. With Kober, 

 we therefore say that ^'shrinking of the earth is no longer hypothesis nor 

 theory, on the contrary it is knowledge built on ascertained facts. '^ 



This j^eriodicity, moreover, leads to the most extraordinary result of 

 all, namely, to times of quickened organic evolution and the pulsing of 

 life, to the peopling of the lands by the denizens of the oceans, an evolu- 

 tion that somewhere and somehow has tended to make it possible for the 

 alg^e of the seas to feed on the air and to clothe the land with verdure ; 

 the latter in turn yields food for the animals forced to emerge from the 

 realm of Neptune, and thus life progresses clominantly upward until it 

 results in reasoning man, the controlling organism of the Psychozoic era. 



My labor of love is now finished. I have told you in the main of the 

 localized geosynclines and the oceanic floodings of the continent. In the 

 following papers of this Symposium you will learn more of how geosyn- 

 •clines are transformed into synclinorial mountain systems, or how vast 

 expanses of inland seas become transformed into glorious mountains, 

 areas scenically grand, geologically most difficult, and structurally highly 

 interesting and significant. From studies in depression I turn you over 

 to studies in uplift. 



