4 
GEOLOGICAL AGENCIES. Q7 
the year, the trade-winds prevail, blowing quite uniformly from the 
eastward, (between northeast and southeast,) except for five to seven 
degrees either side of the equator, which region is subject to calms 
and variables. During the winter months, westerly winds displace 
the regular trades, and blow over the part of the ocean included 
within fifteen or twenty degrees of the equator, extending as far east 
as the Paumotus. Gales often appear in the course of these winds, 
and occasional hurricanes prove destructive to the forests and native 
villages, and give great height and force to the waves. 
a. Rains fall almost exclusively on the windward sides of the 
higher islands; for the moisture brought in with the winds is con- 
densed by the first slopes which they encounter. In consequence 
of this, one side of an island is comparatively dry, with few if any 
streams, while the other is well watered; and denudation is corre- 
spondingly apparent on the opposite slopes. 
j- The usual steepness of the declivities of basaltic islands gives 
great rending and transporting force to the torrents. 
k. Slow decomposition from moisture and atmospheric agents is 
constantly in progress, and this is hastened by the luxuriance of 
vegetation. 
{. The solution of lime by the sea acting upon the corals and 
shells of the reefs, leads to its deposition again along the sea-shores, 
forming a cement to a consolidating limestone, sand-rock, or con- 
glomerate. 
m. As another agent, we mention the great waves of translation, 
which sometimes drive along over the whole extent of an ocean, 
with a rending power far beyond the ordinary oscillations of the 
sea. ‘T'he earthquake of Valdivia in 1837 gave origin to a series 
of these waves of translation, which moved on and made themselves 
felt with serious results at the Sandwich Islands, a distance of more 
than five thousand miles. 
n. The geology of the Pacific islands might be expected to derive 
other peculiarities from the absence of all native mammals excepting 
bats. While at the same time their insular condition does not 
preclude the possibility of fresh-water formations containing fossil 
animals of land and fresh-water origin, and even in some cases the 
fresh-water clam (Unionide), as at the Feejee Islands. 
