NATURAL CHANGE OF COAST-LINE. 399 
marine estuaries, advancing the coast-line, and diminishing the 
area covered by the waters. He has gone beyond this, and in- 
vaded the realm of the ocean by constructing within its borders 
wharves, piers, light-houses, breakwaters, fortresses, and other 
facilities for his commercial and military operations; and in 
some countries he has permanently rescued from tidal overflow, 
and even from the very bed of the deep, tracts of ground ex- 
tensive enough to constitute valuable additions to his agricul- 
tural domain. The quantity of soil gained from the sea by 
these different modes of acquisition is, indeed, too inconsidera- 
ble to form an appreciable element in the comparison of the 
general proportion between the two great forms of terrestrial 
surface, land and water; but the results of such operations, 
considered in their physical and their moral bearings, are sufli- 
ciently important to entitle them to special notice in every com- 
prehensive view of the relations between man and nature. 
There are cases, as on the western shores of the Baltic, where, 
in consequence of the secular elevation of the coast, the sea ap- 
pears to be retiring; others, where, from the slow sinking of 
the land, it seems to be advancing. These movements depend 
upon geological causes wholly out of our reach, and man can 
neither advance nor retard them.* 
* It is possible that the weight of the sediment let fall at the mouths of 
great rivers, like the Ganges, the Mississippi, and the Po, may cause the de- 
pression of the strata on which they are deposited, and hence if man promotes 
the erosion and transport of earthy material by rivers, he augments the weight 
of the sediment they convey into their estuaries, and consequently his action 
tends to accelerate such depression. There are, however, cases where, in 
spite of great deposits of sediment by rivers, the coast is rising. Further, 
the manifestation of the internal heat of the earth at any given point is 
conditioned by the thickness of the crust at such point. The deposits of 
rivers tend to augment that thickness at their estuaries. The sediment of 
slowly-flowing rivers emptying into shallow seas is spread over so great a sur- 
face that we can hardly imagine the foot or two of slime they let fall over 
a wide area in a century to form an element among even the infinitesimal 
quantities which compose the terms of the equations of nature. But some 
swift rivers, rolling mountains of fine earth, discharge themselves into deeply 
scooped gulfs or bays, and in such cases the deposit amounts, in the course of 
a few years, to a mass the transfer of which from the surface of a large basin, 
