300 ANNUAL REPORT SMITHSONIAN INSTITUTION, 193 3 



pected relationship. It is further objected that we do not know 

 of an adequate force for moving the continents over a solid-fluid 

 subcrust. 



While the theory accounts for the formation of the Tertiary moun- 

 tains of the Pacific and the Mediterranean and also accounts for 

 the lack of mountains bordering the Arctic and the Atlantic, it falls 

 down in its explanation of so many other facts that we must reserve 

 judgment as to its merits and accept it at present only as a brilliant 

 attempt to give a general explanation for many scientific facts. 



GRAVITATIONAL SLIDING OF CONTINENTS 



Some years ago Eduard Suess put forward the idea in his epoch- 

 making book, Das Antlitz der Erde, that the mountains of southern 

 and eastern Asia have resulted from the slow creep or gravitational 

 sliding of the great continental mass of Asia toward the bordering 

 deep Pacific Basin. It was in part from this suggestion that F. B. 

 Taylor, of the United States, and Alfred Wegener, of Austria, drew 

 their elaborate continental-drift theories. 



In recent years R. A. Daly, of Harvard, has elaborated on the 

 probabilities of folded mountains resulting from the gravitational 

 sliding of continents. He has cleared up a number of points of op- 

 position and has added much new material. According to his theory 

 the geosynclines bordering the continents cause the crystalline rock 

 crust, composed of the granite shell and the upper frozen layer of 

 basalt, to sink deep into the glassy basalt layer, which has less den- 

 sity than the crystalline rock above. Tension cracks allow the glassy 

 basalt to work up through the crystalline belt and cause it to founder, 

 thus removing the chief source of resistance to the gravitational slid- 

 ing of the continent toward the ocean basin. The light, unconsoli- 

 dated sediments, therefore, resting on the readily deformed basaltic 

 glass, are easily folded and thickened by the advancing continental 

 mass. The more rapid movement of the lands nearer the ocean than 

 of the lands farther inland would cause tension cracks to develop 

 some distance back from the continental border, with block faulting 

 and depression, as, for example, the Great Basin in relation to the 

 Sierras and the Coast Range, and the Triassic basins to the Appa- 

 lachians. Also, the more rapid advance of the continental mass 

 toward a great ocean deep than elsewhere explains the arcuate char- 

 acter of such island festoons as that of the Aleutian Arc and the 

 Japanese Arc. 



Further, according to this theory, as folding of the weak sedi- 

 ments continues, more and more of the underlying crystalline rock 

 is foundered. As time goes on the lower portion of the zone of 

 crumpled sediments is melted, and the great masses of foundered 



