3l8 C. SKOTTSBERG 



j)ossibility that, at some period of its existence, it has formed part of the con- 

 tinent. This is e.g. the case witli the Falkland Islands. A truly oceanic island 

 lacks a continental basement of old, granitic or sedimentary rocks; at least, their 

 presence has not been demonstrated. It is, on all sides, surrounded by deep water 

 and a rise of perhaj:)s thousands of metres is required to bring it into contact 

 with a continent. Mavr (/J^), however, argues that, from a biological viewpoint, 

 every island, whether situated on a continental shelf or not, is oceanic which has 

 received its entire living world across the open ocean — consequently it must be 

 shown that every kind of organism present on the island has or once had the 

 faculty of migrating across the sea and establishing itself, either the species ac- 

 tually found or their ancestors. 



It goes without saying that the answer to the question "continental or oceanic?" 

 should in the first place be looked for in the history of the oceans. With regard 

 to the Pacific our knowledge of its origin and history is incomplete, and even 

 if modern ()ceanograj)hical research has supplied a wealth of information on the 

 hydrography, the nature of the sediments and so on, large parts of the southern 

 Pacific are little known and soundings so few that we cannot form but a very 

 general idea of the bathymetrical conditions and the configuration of the bottom. 

 The northern half is of course far better known. As it is, we must admit that 

 little or nothing has come to light that is opposed to the theory of the perma- 

 nence of the Pacific Ocean. It is, with few exceptions, from the biologists' camp 

 that the theory has been attacked, particularly by phytogeographers; the majority 

 of zoologists seem to accept the conclusions arrived at by physiographers and 

 geologists. It is easy to understand, however, that many biogeographers, struck 

 by the [)er{)lexing disjunctions in the distribution of plants and animals, started 

 to build bridges across wide expanses of sea, in cases with a generosity that led 

 to absurdities. I have no reason to enter into details, our problem concerns Ant- 

 arctica, southern South America and Juan P>rnandez, but even so it seems worth 

 while to (juote a number of modern scientists, mainly geographers and geologists, 

 who have expressed their opinion on the nature and history of the Pacific Ocean. 



Geotectonics of the Pacific Basin. 



H.MI.F.V Willis (2S4) thinks that a suboceanic pressure works against the con- 

 tinents surrounding the Pacific, resulting in an expansion of the suboceanic mass 

 and a deepening of the basin which, in its turn, has a displacing effect on the 

 continental margin. lie summarizes p. 367-368: 



The consideration of the general facts of the geotectonics of the Pacific basin thus 

 leads us to regard the great ocean as a dynamic realm, within which the peculiar char- 

 acteristics of its rocks have facilitated the internal forces of the earth. The effects have 

 i)een as a whole to deepen the basin in conse([uence of the expansion of the under- 

 lying ro( ks. The expansion has in turn crushed the continental margins and raised the 

 great cordilleras. Geologic studies of the mountain ranges have demonstrated that the 

 actual orogenic j)criod began in the Jurassic or possibly somewhat earlier in the Mesozoic. 

 Of the earlier periods we know but little, but the fragmentary records indicate that 

 })eriods of orogenic activity alternated with those of (piiescence. 



