278 ANNUAL riErORT SMITHSONIAN INSTITUTION, 19 2 8 



America are built in the main by the same fundamental process, 

 namely, subsidence of the oceanic areas. This sinking of the oceans 

 brings on subcrustal flowage toward and under the continents, 

 elevating them most along their margins, and at the same time 

 pushing them and the geosynclinal areas inward against the neutral 

 and shield areas of the interior land. 



The repetition from age to age of thu same sort of structures at any given 

 tract on the continent is a fact of absolutely tlie liigliest importance. It indi- 

 cates not only a ixrsistent arrangement of cause and effect, but also a perma- 

 nence of form and environment, which malce of North America an extremely 

 well-defined unit having a definite system of structural laws and responding to 

 repeated thrusts from the direction of each of the adjoining oceans. In this 

 history I can see only an individuality of the continent, its unity, and also its 

 permanence of environment, and I see nothing of the haphazard arrangement 

 which must have followed the random course of a continent floating like a 

 waif on a sea of sial (p. 372). 



Discussing the Wegener and other similar hypotheses, Keith con- 

 cludes (p. 384) : 



I am convinced tliat it is reasonable to accept the theory of thrust against 

 the continent [North America] from all of the surrounding oceans, and also 

 the doctrine that the continental shape and size have been roughly constant 

 from the present day far back into the pre-Cambrian. 



Each major cycle of thrusting is of long endurance, and such 

 " have occurred as a major revolution at least three times since the 

 Cambrian." The fact of such cycles ".seems clear in North 

 America." 



Termier,"'"' director of the Geological Survey of France, says that 

 the German theory has " undeniable charm and real beauty." It is 



a beautiful dream, the dream of a great poet. One tries to embrace it, and 

 finds that he has in his arms but a little vapor or smoke ; it is at the same time 

 both alluring and intangible. 



With Termier and Diener, the writer agrees that Wegener's 

 hypothesis stands upon the very unsound method of departing from 

 the theory of the permanency of position of the earth's greater con- 

 figurations of continents and oceans, and opposing to it one that 

 unites all of the present lands into one enormous continent that en- 

 dured until middle Mesozoic time, wdien it began to break up and 

 the parts to drift into the positions seen to-day. We are on safe 

 ground only so long as we follow the teachings of the law of uniform- 

 ity in the operation of nature's laws. The battle over the theory of 

 the permanency of the earth's greater features introduced by James 

 D. Dana has been fought and won by Americans long ago. In 

 Europe, hoAvever, this battle is not yet fought to a conclusion, since 

 there are leading geologists who still follow Lj'ell and believe in the 



•I" p. Tnrniipr. The Drifting of the Continents, Ann. Rept. Smithson. Inst, for 1924 

 (1925), pp. 219-2.-56. 



