400 NATURAL CHANGE OF COAST-LINE. 
There are also cases where similar apparent effects are pro- 
duced by local oceanic currents, by river deposit or erosion, 
by tidal action, or by the influence of the wind upon the waves 
and the sands of the seabeach. A regular current may drift 
suspended earth and seaweed along a coast until they are caught 
by an eddy and finally deposited out of the reach of further dis- 
turbance, or it may scoop out the bed of the sea and undermine 
promontories and headlands; a powerful river, as the wind 
changes the direction of its flow at its outlet, may wash away 
shores and sandbanks at one point to deposit their material at 
another; the tide or waves, stirred to unusual depths by the 
wind, may gradually wear down the line of coast, or they may 
form shoals and coast-dunes by depositing the sand they have 
rolled up from the bottom of the ocean. These latter modes of 
action are slow in producing effects sufficiently important to be 
noticed in general geography, or even to be visible in the repre- 
sentations of coast-line laid down in ordinary maps; but they 
nevertheless form conspicuous features in local topography, and 
they are attended with consequences of great moment to the 
material and the moral interests of men. The forces which 
and its accumulation ata single point, may be supposed to produce other 
effects than those measurable by the sounding-line. Now, almost all the opera- 
tions of rural life, as I have abundantly shown, increase 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 trans- 
ported by that river to the sea, and of course have strengthened the effects, 
whatever they may be, of thickening the crust of the earth in the Bay of 
Bengal. In such cases, then, human action must rank among geological influ- 
ences. 
To the geological effects of the thickening of the earth’s crust in the Bay of 
Bengal, are to be added those of thinning it on the highlands where the Ganges 
rises. The same action may, as a learned friend suggests to me, even have a 
cosmical influence. The great rivers of the earth, taken as a whole, transport 
sediment from the polar regions in an equatorial direction, and hence tend to 
increase the equatorial diameter, and at the same time, by their inequality of 
action, to a continual displacement of the centre of gravity, of the earth, 
The motion of the globe, and of all bodies affected by its attraction, is modified 
by every change of its form, and in this case we are not authorized to say that 
such effects are in any way compensated. 
