power
of the tides and currents, or to the great movements which alter the
relative level of the land and sea, (Chap. XX.) If, in addition to the
assistance obtained by parliamentary grants for defending Dunwich from
the waves, all the resources of Europe had been directed to the same
end, the existence of that port might perhaps have been prolonged for
several centuries (p. 310.) But in the mean time, the current would have
continued to sweep away portions from the adjoining cliffs on each side,
giving to the whole line of coast its present form, until at length the
town, projecting as a narrow promontory, must have become exposed to the
irresistible fury of the waves.

It is scarcely necessary to observe, that the control which man can
obtain over the igneous agents is less even than that which he may exert
over the aqueous. He cannot modify the upheaving or depressing force of
earthquakes, or the periods or degree of violence of volcanic eruptions;
and on these causes the inequalities of the earth's surface, and,
consequently, the shape of the sea and land, appear mainly to depend.
The utmost that man can hope to effect in this respect is occasionally
to divert the course of a lava-stream, and to prevent the burning
matter, for a season, from overwhelming a city, or some other of the
proudest works of human industry.

If all the nations of the earth should attempt to quarry away the lava
which flowed during one eruption from the Icelandic volcanoes in 1783,
and the two following years, and should attempt to consign it to the
deepest abysses of the ocean, they might toil for thousands of years and
not accomplish their task. Yet the matter borne down to the sea by two
great rivers, the Ganges and Burrampooter, in each quarter of a century,
probably equals in weight and volume the mass of Icelandic lava produced
by that great eruption (p. 282). So insignificant is the aggregate force
exerted by man, when contrasted with the ordinary operations of aqueous
or igneous agents in the natural world.

No application, perhaps, of human skill and labor tends so greatly to
vary the state of the habitable surface, as that employed in the
drainage of lakes and marshes, since not only the _stations_ of many
animals and plants, but the general climate of a district, may thus be
modified. It is also a kind of alteration to which it is difficult to
find anything analogous in the agency of inferior beings; for we ought
always, before