362 A. KEITH OUTLINES OF APPALACHIAN STRUCTURE 



found, however, in calcnlating the shrinkage necessary to account for the 

 folded mountains, that Paleozoic time sn23plies only a small fraction of 

 what is necessary. The time required is so great that other major differ- 

 ences are entailed, such as speed of revolution and its results. Further- 

 more, the great relations of ocean and continent were so substantially 

 the same during the Paleozoic that geologists can not admit major 

 changes of the earth's plan during that era. If new calculations are 

 made, based on the true amount of Appalachian shortening, the discrep- 

 ancy will be thrice as great. The same quantitative difficulty is met by 

 the advocates of lateral thrust from the sea-floors. This also is under- 

 stood to go back to contraction of the earth for its cause. This theory 

 is, therefore, subject to the same limitations of quantity as are the older 

 theories depending on contraction. It must be conceded, however, that 

 there is some lateral thrust from the sea-floors, unless all contraction of 

 the earth is denied -and unless the greater density of the crust beneath 

 the seas is disputed. 



Xo such troubles disturb the advocates of continental creep. Taylor's 

 theory calls for a southward movement of 2,500 miles in the Malay lobe, 

 while Wegener bespeaks 3,000 miles of westward travel for South Amer- 

 ica. Wegener thinks that Xorth America has crowded over against Asia, 

 but the connection of Asia with America through the Aleutian Islands 

 is one of the most beautiful structural units of the globe and clearly per- 

 mits of no accidental piling up of America on eastern Asia. The buoy- 

 ancy of America on the sea of sima was not shared by Asia, for some 

 unexplained reason, so that Asia was left in the lurch. "Westward ho V 

 for America is thus of venerable antiquity. The quiescence of Asia, how- 

 ever, does not appeal to Suess, who assigns to Asia the active and oft- 

 repeated role of a vortex of diastrophism. 



It should be borne in mind that the theory of lateral movement of 

 great masses is not new ; it is the necessary consequence of the shortening 

 observed in mountain ranges. The present theories of continental creep 

 merely extend the movement over vastly greater areas than older theories. 

 All of the theories, hoAvever, unite in one thing: they regard Africa and 

 India as negative elements; even the Wegener theory, which pushes the 

 continents around so freely, has left Africa unmoved. During the 

 troublous times of the Quaternary, according to the Wegener theory, 

 Africa may thus have afl:'orded a safe refuge for the preservation of man, 

 and the theory should have pointed out the desirability of search there 

 for Tertiary man. The present backward condition of the African races 

 might thus be traceable to their freedom from diastrophism and its 



