RISE OF CHRONOLOGY 495 



are found only on the margin of the continents or on continental islands, 

 and all of them do not total more than 1 per cent of the earth's surface. 

 Even though the theory of the permanency of continents and oceanic 

 basins is now of wide acceptance, it does not follow that the continents 

 and oceans have practically retained their present outlines since the be- 

 ginning of the Cambrian. On the contrary, it is held by many geolo- 

 gists — and more so in Europe than in America — that the continents have 

 changed much in form and in area. My studies have convinced me that 

 during the Paleozoic the continents were not only larger in area, but more 

 especially that they were not then, as they are now, drawn out longitudi- 

 nally. Originally there were two immense transverse or latitudinal con- 

 tinents (see figure 1). In the north lay Eria, the great holarctic land, at 

 times uniting the Euro- Asiatic mass broadly with Iceland, Greenland, 

 and North America; in the equatorial region lay Gondwana, extending 

 from western South America across the Atlantic Ocean to unite with 

 Africa, and broadly across the Indian Ocean to embrace peninsular India. 

 Between these transverse lands lay the greater mediterranean, known as 

 Tethys, uniting in the west sparingly with Poseidon (now the North 

 Atlantic) and in the east broadly with the Pacific, the Father of Oceans. 

 Gondwana was broken through in late Mesozoic time by Poseidon and 

 Nereis, which together made the Atlantic, while Eria began to be frac- 

 tured in the Cretaceous, though Europe, Greenland, and North America 

 appear not to have been completely sundered until Miocene time. We 

 therefore have here the phenomenon of oceanic realms enlarging at the 

 expense of the continents. From this and the further evidence of vol- 

 canic activity throughout the geologic ages, it follows that the amount of 

 water on the surface of the earth is greater now than it ever was, because 

 enlarging basins hold increased volumes of water. The water of the en- 

 larging hydrosphere is constantly supplied by the volcanoes and thermal 

 springs, but what the percentage of increase has been since the Cambrian 

 is unknown, though it has been placed as high as 25 per cent. 



DISTURBANCES AND REVOLUTIONS 



The continents periodically undergo elevation and mountain folding, 

 and these times of crustal unrest all occur when the lands are the least 

 flooded. This periodic readjustment in the earth-shell of North America 

 is recorded by at least fourteen times of mountain-making. Eight of 

 these*are of lesser import, and may be spoken of as "disturbances" to dis- 

 tinguish them from the major movements that have long been referred to 

 as "revolutions," of which there are six now named. The latter are also 

 the "critical periods" in the history of the earth when mountains are 



