MATTHEW, CLIMATE AND EVOLUTION 309 



SO marked, oln-ious and universal a feature of the earth's surface that it 

 affords the strongest kind of evidence of the antiquity of the ocean basins 

 and the limits beyond which the continents have not extended. The 

 supposed evidence for greater elevation in the erosion channels across its 

 margin have been shown to be better interpreted as due to "continental 

 creep." The marine formations now found in continental areas have all 

 been deposited in shallow seas. No abyssal deposits have ever been cer- 

 tainly recognized among the geologic formations of the continental plat- 

 form. 



Leaving out of consideration speculative hypotheses as to a formerly 

 smaller amount of water on the surface of the globe, shallower ocean 

 basins in Paleozoic times and different land and water distribution in the 

 older geological periods, it is sufficient for the purposes of this discussion 

 to emphasize the great weight of geological and physiographic evidence 

 for the permanency of the continental masses as outlined by the conti- 

 nental shelf, during the later geological periods, and especially during the 

 Tertiary. 



The present distribution of continents and oceans on the surface of the 

 globe (as outlined by the continental shelf) consists of a great irregular 

 northern mass including Europe, Asia and North America, with three 

 great partly isolated projections into equatorial and southern latitudes, 

 South America, Africa and Australasia, and a smaller Antarctic land 

 mass wholly isolated. The three peripheral continents are isolated from 

 each other and from the Antarctic land by broad and deep oceans, but 

 with the doubtful exception of Australasia, are miited to the central mass 

 by shallow water or restricted land connections. 



A rise of 100 fathoms would unite all the continents and continental 

 islands, except perhaps Australia, into a single mass, but would leave 

 Antarctica, New Zealand, Madagascar, Cuba and many smaller islands 

 separate. A further elevation of five times this amount would not alter 

 materially the boundaries of land and sea. A submergence of 100 fath- 

 oms would isolate the three southern continents, and cause shallow seas 

 to spread widely over the interior of all the continental masses, reducing 

 some of them to isolated fragments or archipelagoes. 



Such cyclic alternations of emergence and overflow are recognized by 

 many geologists as the dominant feature of the earth's history, corre- 

 sponding to the succession of periods into which geologic time is divided. . 

 The greater disturbances resulting in folding, faulting and mountain 

 making, while involving much greater changes of level, affect more lim- 

 ited areas, adjacent to lines of unstable equilibrium, especially along the 

 borders of the continental platforms. 



