2o6 THE PHYSICAL GEOGRAPHY OF THE SEA. 



of themselves scarcely possess the power of locomotion. Yet tliev 

 have power to put the whole sea in motion, from the equator to 

 the poles, and from top to bottom. But we have yet to inquire 

 how far may currents be due to the derangement of equilibrium 

 arising from the change of specific gravity caused by the secre- 

 tions of the myriads of marine animals that are continually at 

 work in various parts of the ocean. These little creatures ab- 

 stract from sea water solid matter enough to build continents of 

 And, also, we have to remember as to the extent to which equi- 

 librium in the sea is disturbed by the salts which evaporation 

 leaves behind. Thus, when we consider the salts of the sea in one 

 point of view, we see the winds and the marine animals operating 

 upon the waters, and, in certain parts of the ocean, developing by 

 their action upon the solid contents of the same those very prin- 

 ciples of antagonistic forces which hold the earth in its orbit, and 

 preserve the harmonies of the universe. 



487. In another point of view, we see the sea-breeze and the 

 Dynamical force de- sca-shcll, 1X1 performing their appointed offices, act- 

 nved from. • j^g g^ ^g ^^ gj^^ ^.-g^ ^^ ^ rcciprocating motion in 



the waters ; and thus they impart to the ocean dynamical forces 

 also for its circulation. The sea-breeze plays upon the surface ; 

 it converts only fresh water into vapor, and leaves the solid mat- 

 ter behind. The surface water thus becomes specifically heavier, 

 and sinks. On the other hand, the little marine architect below, 

 as he works upon his coral edifice at the bottom, abstracts from 

 the water there a portion of its solid contents ; it therefore be- 

 comes specifically lighter, and up it goes, ascending to the top with 

 increased velocity, to take the place of the descending column, 

 which, by the action of the winds, has been sent down loaded with 

 fresh food and materials for the busy little mason in the depths 

 below. Seeing, then, that the inhabitants of the sea, with their 

 powers of secretion, are competent to exercise at least some degree 

 of influence in disturbing equilibrium, are not these creatures en- 

 titled to be regarded as agents which have their offices to perform 

 in the system of oceanic circulation, and do they not belong to its 

 physical geography ? Their influences upon the economy of the 

 sea are like those outstanding quantities which the astronomer 

 finds in the periods of heavenly bodies. He calls them perturba- 

 tions; for short, or even during considerable intervals, their effects 



