DERIVATION OF THE FLORA AND FAUNA 3I9 



Willis did not question the permanence of the basin; what interests us here 

 more particularly is his belief in the instability of the marginal regions. 



In H. E. Gregory's view the Pacific basin inside the deep troughs is an old 

 sink and it follows that all the islands within this sink are truly oceanic. Con- 

 sidering geological evidence alone there has been no significant change in the 

 position of Polynesian land masses since Pleistocene, most likely since early Ter- 

 tiary time: "There is no geologic evidence that any Polynesian island stood in 

 Jurassic or Cretaceous seas" (775. 1673). Still he thought that due regard should 

 be taken to objections raised by other branches of science, and he did not extend 

 the unaltered permanent basin outside the deep troughs. When, a little later, 

 another prominent geologist, J. W. Gregory (116), expressed a different opinion, 

 this attracted a good deal of attention. The Pacific had, he says, been claimed 

 to have existed in its present shape and size throughout geological time, a hypo- 

 thesis almost universally adopted by geophysicists and geologists, but from 

 a biological viewpoint this theory did not satisfy. GREGORY was no believer in 

 large-scale transmarine migration of either plants or animals and consequently 

 inclined to consider the arguments put forth by the opponents to the permanence 

 theory. He counted with a number of Pacific seas separated by stretches of land, 

 and he looked upon the region where atolls serve as proofs of subsidence, a sub- 

 sidence which gradually enlarged the basin until it reached its present size, as 

 originally continental. 



Andrews [6) who was a firm believer in successful transoceanic migrations 

 of all kinds of organisms and knew more about geology than most biogeogra- 

 phers, shared H. E. Gregory's opinion: islands situated within the area bounded 

 by the ocean deeps such as Hawaii, Marquesas, Society and Juan Fernandez, all 

 differing in their geological structure from the continents, are oceanic. Parts 

 of Andrews' interesting paper deserve to be quoted here. 



An examination of the continental blocks proper and the great western island 

 arcs suggests that they have had similar histories, whatever great differences may other- 

 wise exist between them. Japan, Eastern Australia, New Zealand, New Guinea, Fiji . . . 

 may be taken as examples. Each has a foundation of ancient folded and metamor- 

 phosed sediments, such as conglomerates, grits, quartzites, sandstones, slates, shales, 

 and limestones, and each of these foundations has been subjected to marked plutonic 

 intrusions of granitoid nature. Upon this foundation have been accumulated sediments 

 similar to those mentioned above, together with lavas not only of basic but also of 

 acid types. These, in turn, have been folded, overthrust, and invaded by plutonic rocks. 

 This generalization is true even though as yet no consensus exists concerning the age, 

 or ages, of the folded sediments and plutonic intrusives of the foundadon rocks. It 

 would appear, however, that the foundation rocks of the island arcs which occur mar- 

 ginally to the continents of Asia and Australia are not as old as the earliest members 

 of the continental nuclei. This leads to the consideration of island arcs situated more 

 centrally within the Pacific Ocean. P'or this purpose, these may be considered as in- 

 cluding all the Pacific islands lying oceanward of the great island arcs mentioned above. 

 The principal examples include the Hawaiian Islands, the Marquesas, Juan Fernandez, 

 Easter Island, the Society Islands, the Cook Group, the Line Group, Micronesia, Samoa, 

 and the Ladrone, Caroline, and Pellew groups; Tonga and the Hebrides occupy a 

 peculiar position, mentioned below (p. 202—3). 



