26 PACIFIC ISLANDS. 
III. GEOLOGICAL AGENCIES IN THE PACIFIC. 
The following brief statement of the several sources of geological 
changes and effects in the Pacific, is here introduced, to aid the reader 
in apprehending more clearly the particular facts presented by the 
different groups of islands. 
a. As the islands are situated within or near the tropics, the moun- 
tains are free from the rending and degrading action of frosts or ice. 
At the same time, a luxuriant vegetation throws a protection even 
over the steepest declivities. Bluffs, with a talus or slope of fallen 
fragments at foot, are therefore rarely met with. 
6. Volcanic or igneous action having been rife in this ocean, the 
results of eruption and of earthquakes, with the usual attendant cir- 
cumstances, are common. 
c. The growth of coral not only forms islands, but produces barriers 
around basaltic islands, which act as breakwaters, or confine the sedi- 
ment flowing from the hills. 
d. The action of the waves and swell of the sea, are agents of great 
force in insular lands, where so large a line of coast compared with 
the area, is exposed to their action. 
e. The currents of the ocean are but little appreciable at the sur- 
face, and have left few traces of their influence, except in the trans- 
port of seeds, and floating logs carrying occasionally an attached stone 
and some sea-shore animals. 
fj. Around many islands, other more active currents exist, owing 
in part to the reefs and the configuration of the land, which currents 
have an important influence on the growth and distribution of coral, 
and the characters of shores. 
g. The tides in the Pacific are comparatively feeble in their effects. 
Through the eastern part of Polynesia they are but two or three feet 
in height; about Samoa, they are four feet; at the Feejee Islands, six 
feet; at New Zealand, eight feet. ‘They have a decided influence on 
the height of growing reefs, and upon the forms of the shores of coral 
islands. 
h. The winds in connexion with the swell of the sea exert much 
influence on the features of a coast, drifting the beach-sands into 
hills on the parts of the islands exposed; and this effect is strikingly 
apparent on coral reefs and islands. ‘Through the greater part of 
