160 R. A. Daly — Problems "of the Pacific Islands. 



than his colleague observing in continental interiors. The 

 topographic development of oceanic islands is in general so 

 peculiar that the trained physiographer will be amply repaid 

 for any labor he may expend on them. 



The physiography of the sea itself oifers important questions 

 which are best answered by observers along the island shores. 

 The depths of the great ocean currents, their variations from 

 the surface downward, their power to transport bottom sedi- 

 ment at different depths, their relation to the submarine shelves 

 which encircle most islands, the water movements in the 

 numerous island lagoons, the temperatures, salinity, and detailed 

 chemistry of the subsurface waters within reefs and outside 

 them — are all topics on which much information is needed. 

 The same is true of the erosive etficiency of open-ocean waves, 

 concerning which almost nothing quantitative has yet been 

 determined by observers on oceanic islands. 



However, for general science the origin of the islands and 

 the origin of their living inhabitants have the deepest signi- 

 ficance. The geology and biology of the islands are important 

 to a degree certainly not to be measured by the total land 

 area involved. "When the vast labor of determining all their 

 faunas and floras is once brought to completion, the biology of 

 the globe as a unit will be profoundly affected. A host of 

 questions regarding the physiology, adaptations, dispersals, 

 mutual relations, phylogeny and ontogeny of the plants and 

 animals (including man) press for answer. Many of the answers 

 must sway opinion as to biological essentials the world over. 



Of these matters I am not competent to speak with authority. 

 Yet it may tend to make the advisability of immediate explor- 

 ation in the Pacific basin more vivid if I try to present concrete 

 geological problems in some detail. With your indulgence, 

 therefore, the origin of the islands themselves will be briefly 

 discussed, with the definite purpose of illustrating the need for 

 future investigation on the large scale. 



The Pacific islands, which are not close to the continents, 

 may be divided into five groups, according to the character of 

 their rocks. A small number are composed of rock types 

 characteristic of large areas in the continents, like granite, 

 gneiss, schist, serpentine, and deformed sediments. Some of 

 the high islands show none but volcanic constituents. Most 

 of the low islands, in their visible parts, are composed wholly 

 of limestone. Many of those betraying an essentially volcanic 

 origin have limestones interbedcled with, or resting on, the 

 lava formations. Other composite islands, few in number, 

 include continental rocks, volcanic rocks, and limestones of 

 recent dates of formation. Each of the five groups has its own 

 problems, but the fundamental questions now to be considered 



