ANCIENT PORTALS OF THE EARTH 393 



ANCIENT POETALS OF THE EARTH 



By Professor JAMES PERRIN SMITH 



STANFORD UNIVERSITY, CALIFORNIA 



Portals Defined. — A study of the distribution and relationships of 

 ancient marine faunas shows that there have been certain critical areas 

 through which these faunas were connected from time to time. These 

 critical areas are depressions on or between continental masses, and are 

 invariably regions of permanent instability of the earth's crust, where 

 mountain-making and the accompanying volcanic and earthquake dis- 

 turbances have been prevalent. 



When these areas were depressed below sea-level, they formed straits, 

 or channels, connecting sea-basins, and affording avenues for inter- 

 migration of marine faunas. When they were elevated, they formed 

 barriers impassable to the dwellers in the sea. Thus neither the name 

 strait nor barrier is applicable to them as a general term. Therefore 

 the name portal is selected, as indicating a gateway that may be either 

 open or closed, and still retain its identity. 



Of the portals that were important in the ancient world only three 

 are now open: the North Pacific portal, of which Bering Strait is a 

 shrunken remnant; the Iberian, still recognizable in the Strait of 

 Gibraltar; the Malaysian, seen in the inter-island passages in the East 

 Indian Archipelago. And one has shifted its position, growing from an 

 arm of the sea into the noble expanse of the Indian Ocean. 



One still shows its nature as a portal in the narrow strip of land 

 joining the two Americas. The others are now concealed as parts of 

 continental masses, namely the Crimean, the Asia Minor portal, and the 

 Bokharan, revealing their nature as former arms of the sea only in the 

 extinct marine fossils now buried in their sediments. 



Still other bodies of water that loom up large in our present-day 

 geography, as the North Atlantic and the South Atlantic, too wide to be 

 called merely passages, or to be differentiated from the main ocean by a 

 special name, did not even exist in the ancient days. 



These great changes have been wrought chiefly by the world-wide 

 Tertiary mountain building, and the accompanying, or causing, dis- 

 turbances of the continental areas. Also there was much readjustment 

 in the late Paleozoic topographic revolution, and in the late Jurassic 

 Cordilleran revolution. 



Paleogeography. — In recent years the reconstruction of ancient 

 physical geography has been a favorite field of research, not to say of 

 speculation, of geologists; paleontologists, too, have taken their part in 



voii. Lxxx. — 27. 



