The Evolution of the Universe 



23 



Sea. The Gulf Coast of North America is the site of a geosynchne 

 which has persisted since Cretaceous time. The Coast Ranges of 

 the Western United States are folded and faulted strata representing 

 a geosynchne which originated in Jurassic time and continued 

 through the Cretaceous into late Cenozoic time (King, 1959). In 

 the Pliocene and Pleistocene epochs, relatively recently geologically 

 speaking, the sediments of this geosynchne were greatly deformed 

 and uplifted to form parts of the Coast Ranges. 



Mountain chains, island arcs, and geosynclines occur chiefly 

 along continental margins or around old shield areas ( Fig. 9 ) . This 



Fig. 9. Mountain and island arcs and the continental fracture system active 

 at the present. (After J. T. Wilson.) 



distribution is one of the chief points used by J. T. Wilson (1959) 

 in his postulate that continents have enlarged through geologic 

 time by the addition of geosynclinal sediments to primeval "shield" 

 areas or nuclei of sialic material. 



Umbgrove (1947) believed that these arcs of elevated areas and 

 troughs result from crustal buckling created by hypothetical convec- 

 tion currents in the mantle. He suggested that deep in the mantle, 



