DARWIN'S THEORY OF CORAL REEFS 327 



proximity of an area of metamorphic rocks, while a series of 

 plutonic rocks have recently been described from Tahiti. 



Thus, according to Mr. Speight,* there appears to be geo- 

 logical evidence of the former extension of continental con- 

 ditions over a large area of the mid-Pacific region. As he 

 remarks, it is highly probable that many volcanic islands 

 classified as oceanic will ultimately have to be looked upon 

 as built up on the remnants of a continental area. We may 

 imagine that a large land area or continent covered the greater 

 part of the present Pacific Ocean in Palaeozoic and early 

 Mesozoic times, and that there was a subsidence during later 

 Mesozoic and Tertiary times with more recent local elevations. 



Professor Haug,f discusses the Pacific problem from 

 another point of view. His studies of the geosynclinals, which 

 he calls the essentially mobile regions of the earth's crust, 

 led him to the conclusion that the circumpacific geosynclinal 

 implied the former existence of a continent in place of the 

 present Pacific Ocean. 



The well-known parallelism of the different groups of Pacific 

 islands has likewise been utilised in support of the same 

 theory. It may be explained by the supposition that these 

 islands are either the remnants or the initial stages of a 

 series of mountain chains. J The Funafuti boring results seem 

 to point to the first of these as the more likely assumption. 



That Darwin's theory of subsidence still meets with a good 

 deal of determined opposition by the believers of the per- 

 manence of ocean basins may be gauged from Sir John 

 Murray's writings on the structure and origin of coral reefs. 

 I think it is unnecessary for me to discuss the bearings of his; 

 arguments on the American problems raised in this chapter, 

 because, in the first place, it seems probable that both Mur- 

 ray's hypothesis of elevation and Darwin's of subsidence may 

 be applicable to certain cases, and, secondly, because a Pacific 

 continent in the sense of Button, Pilsbry and Baur cannot 

 evidently be cited in support of most of the older Tertiary 

 affinities between Asia and North America that I have alluded 



* Speight, E., " Petrological Notes on Eocks from Kermadec Islands," 

 pp. 244250. 



t Haug, E., " Geosynclinaux et aires continentales," p. 646. 

 t Arldt, T., " Parallelismus d. Kusten v. Siidamerika." 



