Building of the Marquesas and Tortugas Atolls, etc. 67 



There is abundant evidence of differential crustal movement in the tropi- 

 cal Pacific similar to that indicated for the West Indies. E. C. Andrews^ 

 and C. Elschner^ have both described warping or tilting, the former for the 

 Fijis, the latter for the Pacific more or less in general. Agassiz described 

 an elevated atoll, Makatea, in the Paumotus, and Andrews has given a 

 detailed description of the elevated atoll of Mango, Fijis. The old reefs 

 have been subjected to differentiated earth movement, so that in certain 

 places old atolls, such as Rangiroa and others in the Paumotus, now stand 

 at or near sea-level, while other atolls have been uplifted to heights as great 

 as 230 feet in Makatea and 600 feet in Tuvuth^, Fijis. In other areas 

 there has been depression, Bora-Bora, for instance, as Dana, P. Marshall, 

 and more recently W. M. Davis, have shown. 



In conclusion it will be said regarding the Pacific coral reefs: (i) Atolls 

 are not formed by solution, but by constructional geologic agencies; (2) there 

 was in the tropical Pacific a great development of Pleistocene and perhaps 

 late Tertiary reefs which have subsequent to their formation been sub- 

 jected to extensive differential crustal movement; (3) these deformed older 

 reefs are frequently the basement of the Recent reefs. Although important 

 contributions have already been made to the study of Pleistocene and 

 Recent oscillation and deformation in the Tropical Pacific, there is great 

 need for more extensive and more detailed investigations of this phase of 

 the coral-reef problem in order to ascertain more accurately the relations 

 of the older to che Recent reef series. 



1 Notes on the limestones and general geology of the Fiji Islands; Bull. Mus. Comp. Zool., vol. 38, PP^ 

 27-30. 1900. 



* Corallogene Posphat-Inseln Austral-Oceaniens, pp. 1S-19. Lubeck. 1913. 



