320 



SKOTTSBERG 



Field observations show that those islands have had histories which present marked 

 diftercnces from those of the continents and their marginal island arcs. 'J'hus, they 

 appear to be comjiosed almost entirely of volcanic material, mainly basic, together with 

 "coral reef" formations, whereas granitoid intriisives and acid lavas are lacking, to- 

 gether with the sediments invarial)ly associated with "continental" areas. And not only 

 is this so, but the volcanic ejectamenta of these inner groups do not appear to con- 

 tain fragments of granitoids and sediments such as might be expected from volcanos 

 discharging through a foundation of rock formations such as compose the continents 

 (P- 203). 



Another interesting feature is the ])eculiar topograj)hy of that portion of the Pacific 

 floor which sej)arates the great island arcs and lands of "continental'' character from 

 the more central grouj)s. Thus, on the American side of the Pacific, the "continental" 

 lands are separated from the groups — such as Hawaii, the Marcjuesas, the Society Is- 

 lands, and Juan I'crnandez — by a series of deep discontinuous ocean trenches, prac- 

 tically collinear (j). 203). 



The question is whether these trenches are of quite the same nature and 

 date from the same j^eriod as the deeper trenches arranged oceanward from the 

 great western island arcs. It is unfortunate for the advocates of a "continental" 

 origin of the Juan Fernandez flora that these islands are situated on the wrong 

 side of the trench. However, the Galapagos Islands occupy a similar position, 

 and still they have been claimed, on good grounds, once to have been united 

 with Central America. In this connection another quotation from ANDREWS with 

 regard to the New Hebrides and Tonga is of interest. 



Island groups which are difficult to place exactly in this scheme are the New 

 Hebrides, Tonga, and possibly the Pellews and the Ladrones. A profound deep lies 

 between New Caledonia and the New Hebrides, and this is suggestive of a noncon- 

 tinental origin of the group. On the other hand, the occurrence of mineral deposits 

 such as copj)er, iron, and nickel, of large kauri, fig, myrtaceous, and other trees, and 

 of animals such as lizards, turtles, ducks, pigeons, and parrots, suggests that they may 

 well have formed, at some earlier time, j)ortions of a continental margin which later 

 be< amc involved in a j)Owerful movement within the marginal Pacific, resulting in the 

 gradual submergence of these outer ))ortions, the present Hebrides, Tonga, and so on, 

 being built upon su( h sinking area. This certainly is suggested for the New Hebrides 

 and for Tonga, while the Pellew and Ladrone islands also have had complex histories, 

 which would well repay close attention, in their structural, petrological and biological 

 aspects (p. 203). 



An additional j)C)int of interest is the association of great ocean deeps with youthful 

 volcanic zones, and inasnuu h as the trough and crest of an earth undulation are parts 

 of the same strut ture, it is a legitimate inference that the great Pacific deeps or trenches 

 are relatively youthful structures (p. 203). 



Andkkw.s summarized his idea of the Pacific basin in a number of points, 

 which, with very slight verbal alterations, form the introduction to his paper on 

 the origin of the Pacific insular floras (7. 613-14): 



1. The continents bordering the Pacific have been larger, at various times, than 

 they are at |)resent. 



2. The great bordering island arcs of the Pacific — such as the Aleutians, Japan, 

 the IMiilippines. the Netherlands Fast Indies, New (Guinea, Fiji, New Caledonia, and 

 New Zealand— have been connected directly with the continental lands. Certain of these 



