The Earth as Modified by Human ActionMarsh, George P. (George Perkins)
History
The Earth as Modified by Human Action
Marsh, George P. (George Perkins)
Conservation of natural resources; Human geography; Nature -- Effect of human beings on; Physical geography
The author of this pamphlet has chosen as a motto a passage from the
Vulgate translation of Job, which is interesting as showing accurate
observation of the action of the torrent: "Mons cadens definit, et saxum
transfertur de loco suo; lapides excavant aquae et alluvione paullatim
terra consumitur."--Job xiv. 18, 19.
The English version is much less striking, and gives a different sense.
The recent date of the change in the character of the Mella is
contested, and it is possible that, though the extent of the revolution
is not exaggerated, the rapidity with which it has taken place may have
been.]
There is one effect of the action of torrents which few travellers on
the Continent are heedless enough to pass without notice. I refer to the
elevation of the beds of mountain streams in consequence of the deposit
of the debris with which they are charged. To prevent the spread of sand
and gravel over the fields and the deluging overflow of the raging
waters, the streams are confined by walls and embankments, which are
gradually built higher and higher as the bed of the torrent is raised,
so that, to reach a river, you ascend from the fields beside it; and
sometimes the ordinary level of the stream is above the streets and even
the roofs of the towns through which it passes. [Footnote: Streffleur
quotes from Duile the following observations: "The channel of the
Tyrelese brooks is often raised much above the valleys through which
they flow. The bed of the Fersina is elevated high above the city of
Trent, which lies near it. The Villerbach flows at a much more elevated
level than that of the market-place of Neumarkt and Vill, and threatens
to overwhelm both of them with its waters. The Talfer at Botzen is at
least even with the roofs of the adjacent town, if not above them. The
tower-steeples of the villages of Schlanders, Kortsch, and Laas, are
lower than the surface of the Gadribach. The Saldurbach at Schluderus
menaces the far lower village with destruction, and the chief town,
Schwaz, is in similar danger from the Lahnbach."--Streffleur, Ueber die
Wildbuche, etc., p. 7.] The traveller who visits the depths of an Alpine
ravine, observes the length and width of the gorge and the great height
and apparent solidity of the precipitous walls which bound it, and
calculates the mass of rock required to fill the vacancy, can hardly
believe that the humble brooklet which purls at his feet has been the
principal agent in accomplishing this tremendous erosion. Closer
observation will often teach him, that the seemingly unbroken rock which
overhangs the valley is full of cracks and fissures, and really in such
a state of disintegration that every frost must bring down tons of it.
If he computes the area of the basin which finds here its only
discharge, he will perceive that a sudden thaw of the winter's deposit
of snow, or one of those terrible discharges of rain so common in the
Alps, must send forth a deluge mighty enough to sweep down the largest
Public-domain text, read in full here on John Shaqi.
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