CHAPTER XII 
AGENTS AT WORK IN THE OCEAN 
Agents at Work. — The ocean, like the land, is a seat 
of geological change; but while the principal action on 
land is that of destruction, in the sea the main work is 
deposition and construction. Yet along the coast line 
there is constant erosion. This is of great importance. 
The oceanic agents that are engaged in the double task 
of tearing down and building up, are waves, tides, 
ocean currents, animals and plants. The work of 
construction in which these are constantly engaged, 
is greatly aided by the material which rivers are 
bearing into the sea. : 
Chemical Work. — Dissolved in the sea water are vast 
quantities of rock material, which have been taken 
from the land by means already described. In some 
places these are being precipitated from solution in the 
form of chemical deposits; but so far as we are able to 
tell from our present knowledge of the sea bottom, this 
action is comparatively of little moment. By far the 
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