Association of American G'eologists and Naturalists. 311 
rapid to permit the growth of the coral to keep the islands at the sur- 
face: that the subsidence south of this line, where high islands prevail, 
was less than on the line, and still less than to the north of it. The 
large area of subsidence thus indicated, is not less than five thousand 
miles long and three thousand wide, and covers at least fifteen millions 
of square miles. He also alluded to the singular fact that the longer 
diameter of this area of subsidence corresponded to the trend of the 
Navigator, Society and Sandwich Island groups, and the low or coral 
archipelago. 
As present opinions seem to require a balance motion in changes 
of elevation, he suggested that inasmuch as the tertiary rocks of the 
Andes and North America indicate great elevations since their deposi- 
tion, that possibly during this great Pacific subsidence, America, the 
other scale in the balance, was in part undergoing as great or greater 
elevation. The absence of corals from the western tropical parts of 
this continent, was explained by reference to the extratropical currents 
before alluded to. | 
The President enquired of Mr. D. if he considered this subsi- 
dence to have taken place equally over the entire area. 
Mr. D. replied, that it could hardly be expected that this effect 
should have been eractly uniform, considering the vastness of the 
area, but that considered as a whole it must have been nearly 
uniform. 
The President objected to the supposition of Mr. Dana, that 
this vast amount of subsidence was due to the gradual refrigera- 
tion of the earth from a heated state; he thought it susceptible 
of mathematical demonstration that the amount of subsidence 
was too slight to account for the changes which must have taken 
place in the Pacific. Indeed, the earth must have acquired a 
nearly statical equilibrium of temperature before the existence of 
the corals, which probably did not make their appearance until 
the post-tertiary period. 
Mr. Redfield said he had been much gratified with Mr. Dana’s refer- 
ences to the fixed memorials of the warm currents in the Pacific, as af- 
forded in the coral formations. Previous to the sailing of the Exploring 
Expedition he had the satisfaction of reviewing with Mr. Dana, partly in 
reference to a great dynamical question which regards the currents of 
the atmosphere and the ocean, some of the evidence which he, Mr. R. 
had before obtained of the character and courses of the great system 
of currents in the Pacific, and of the low temperature of the extratropi- 
cal currents which sweep towards the equator along the western coasts 
