388 NATURAL CHANGE OF COAST-LINE. 



beyond this, and invaded tlie realm of tlie ocean by constructing 

 within its borders wharves, piers, light-houses, breakwaters, for- 

 tresses, and other facilities for his commercial and mihtary opera- 

 tions ; and in some countries he has permanently rescued from 

 tidal overflow, and even from the very bed of the deep, tracts of 

 ground extensive enough to constitute valuable additions to his 

 agricultural domain. The quantity of soil gained from the sea 

 by these different modes of acquisition is, indeed, too inconsider- 

 able 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, con- 

 sidered in their physical and their moral bearings, are sufficiently 

 important to entitle them to special notice in every comprehen- 

 sive 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 appears 

 to be retiring ; others, where, from the slow sinking of the land, 

 it seems to be advancing. These movements depend upon geo- 

 logical causes wholly out of our reach, and man can neither ad- 

 vance 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 com- 

 pression and consequently the depression of the strata on which they are de- 

 posited, and hence if man promotes the erosion and transport of earthy ma- 

 terial by rivers, he augments the weight of the sediment they convey into 

 their estuaries, and therefore 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 surface 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, and its accumulation at a single point, may be 

 supposed to produce other effects than those measurable by the sounding-line. 

 Now, almost all the operations of rural life, as I have abundantly shown, in- 

 crease the liability of the soil to erosion by water. Hence, the clearing of the 

 valley of the Ganges, for example, by man, must have much augmented the 

 ■quantity of earth transported by that river to the sea, and of course have 



