_ Mr. Dana on Areas of Subsidence in the Pacific, §c. 131 
land. The peculiar trend of the east coast of South America 
carries off to the northward much of the usual south intratropical 
current, and it is therefore less distinct in its effects, than the 
northern intratropical or Gulf Stream. 
We have hence the remarkable fact, that the coral zone is fifty 
degrees wider on the eastern than on the western coasts of our 
continents. Such is the effect of the ocean currents in limiting 
the distribution of marine animals. ‘These facts will be brought 
out more fully in the reports of the Exploring Expedition. 'The 
important bearing of these facts upon the distribution of fossil 
species is too apparent to require more than a passing remark. 
The many anomalies which have called out speculations as to 
our globe’s passing through areas in space of unequal tempera- 
tures are explained without such an hypothesis. Instead of look- 
ing to space for a cause, we need not extend our vision beyond 
the coasts of our continents. 
Arr. XVI.—On the Areas of Subsidence in the Pacific, as indi- 
cated by the Distribution of Coral Islands ; by James D. Dana, 
Geologist of the United States Exploring Expedition,—with 
a map.* » 
[Read before the Association of American Geologists and Naturalists, at Albany, 
April 29, 1843.] 
Tue theory of Mr. Darwin with regard to the formation of 
atolls, or annular coral islands, has been fully confirmed by the 
investigations of the Exploring Expedition; but his regions of 
subsidence and elevation, and the conclusion that these changes 
are now in progress, appear to have been deduced without suffi- 
cient examination. Observations at a single point of time can- 
not determine whether such changes are in progress; they can 
only assure us with regard to the past. A series of examinations 
for years in succession is necessary to enable us to arrive at the 
grand deduction that the land in any part of our globe is now 
undergoing a gradual change of elevation. The views of. Mr. 
Darwin respecting the rise of the South American coast, as well 
* This map contains the track of the Exploring Squadron, and was intended to 
illustrate the article on the Exploring Expedition, published in our last number, 
but was unavoidably postponed.—Eps. 
