DARWIN’S THEORY OF CORAL REEFS 827 
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.$ 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 Hutton, 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, R., “ Petrological Notes on Rocks from Ivermadec Islands,” 
pp. 244—250. 
t Haug, E., “ Geosynclinaux et aires continentales,” p. 646. 
t Arldt, T., “ Parallelismus d. Ktisten v. Siidamerika.” 
