394 THE POPULAR SCIENCE MONTHLY 



this, since ancient continents can be outlined only by the distribution of 

 the faunas and floras of the land, and ancient seas can be traced only in 

 the remains of petrified inhabitants of the waters. 



In the Book of Genesis we read : " And God said, Let the waters 

 under the heaven be gathered together into one place, and let the dry 

 land appear; and it was so. And God called the dry land Earth; and 

 the gathering together of the waters called He seas : and God saw that 

 it was good." This is certainly the shortest account of the origin of 

 continents and seas, and probably as good as any. But we do not any 

 longer think that it all happened at one time. 



Since we can know definitely the geology of only that part of the 

 earth which is now land, and since we know the underlying strata of 

 only a small part of that, we can only conjecture concerning the history 

 of regions now buried under the oceans. No one man, nor group of men, 

 is qualified to make a dogmatic statement as to the origin of continents 

 and seas, such as that quoted above from Holy Writ. There is ample 

 room for differences of opinion, starting from the same facts. Conse- 

 quently, geologists and physical geographers are divided into two 

 camps. One holds that the major divisions of land and sea were always 

 as they now are; this is the doctrine of permanence of continental 

 plateaus and oceanic basins. The other group advocates the idea of 

 constant change in the position of land masses and oceanic troughs. To 

 them the grand features of the earth do not bear the marks of hoary 

 antiquity, but are youthful characters, due to rather modern diastro- 

 phism of the crust. 



The truth probably lies somewhere between the two extremes, and 

 the differences between the two camps consist rather in statement than 

 in fundamental doctrine. Even the most conservative upholders of the 

 theory of permanence admit that some of the continental areas have 

 been covered, in the past, by seas of almost oceanic size and depth. And 

 the most radical advocates of the shifting of lands and seas believe that 

 some of the continental masses have always been continents, and that 

 some of the great depressions have always been oceans. 



Further, it becomes plainer, as paleogeographic studies go deeper 

 into the history of the earth, that the dominant ancient features are not 

 obliterated by later changes, but are merely obscured. Continents that 

 were dismembered have been united again ; seas that existed in the early 

 days have recurred. Which is to say that whether continental plateaux 

 and oceanic troughs have been permanent or not, the regions of dias- 

 trophism have been permanent, that when crumpling and dislocation of 

 the earth's crust have once started, they have kept up with recurrent 

 activity all through the succeeding ages. 



The ancient portals all lie in regions where the Tertiary mountain 

 folds touch the great lines of crumpling begun in the late Paleozoic 

 topographic revolution. The present distribution of continental pla- 



