Wonders of Earth, Sea and Sky | Page 6

this hard to believe? Look at the crumbling cliffs around old
England's shores. See the effect upon the beach of one night's fierce
storm. Mark the pathway on the cliff, how it seems to have crept so
near the edge that here and there it is scarcely safe to tread; and very
soon, as we know, it will become impassable. Just from a mere
accident, of course,--the breaking away of some of the earth, loosened
by rain and frost and wind. But this is an accident which happens daily
in hundreds of places around the shores.
Leaving the ocean, look now at this river in our neighborhood, and see
the slight muddiness which seems to color its waters. What from? Only
a little earth and sand carried off from the banks as it flowed,--very
unimportant and small in quantity, doubtless, just at this moment and
just at this spot. But what of that little going on week after week, and

century after century, throughout the whole course of the river, and
throughout the whole course of every river and rivulet in our whole
country and in every other country. A vast amount of material must
every year be thus torn from the land and given to the ocean. For the
land's loss here is the ocean's gain.
And, strange to say, we shall find that this same ocean, so busily
engaged with the help of its tributary rivers in pulling down land, is no
less busily engaged with their help in building it up.
You have sometimes seen directions upon a vial of medicine to "shake"
before taking the dose. When you have so shaken the bottle the clear
liquid grows thick; and if you let it stand for awhile the thickness goes
off, and a fine grain-like or dust-like substance settles down at the
bottom--the settlement or sediment of the medicine. The finer this
sediment, the slower it is in settling. If you were to keep the liquid in
gentle motion, the fine sediment would not settle down at the bottom.
With coarser and heavier grains the motion would have to be quicker to
keep them supported in the water.
Now it is just the same thing with our rivers and streams. Running
water can support and carry along sand and earth, which in still water
would quickly sink to the bottom; and the more rapid the movement of
the water, the greater is the weight it is able to bear.
This is plainly to be seen in the case of a mountain torrent. As it foams
fiercely through its rocky bed it bears along, not only mud and sand and
gravel, but stones and even small rocks, grinding the latter roughly
together till they are gradually worn away, first to rounded pebbles,
then to sand, and finally to mud. The material thus swept away by a
stream, ground fine, and carried out to sea--part being dropped by the
way on the river-bed--is called detritus, which simply means
_worn-out_ material.
[Illustration: A MOUNTAIN TORRENT.]
The tremendous carrying-power of a mountain torrent can scarcely be
realized by those who have not observed it for themselves. I have seen
a little mountain-stream swell in the course of a heavy thunderstorm to
such a torrent, brown and turbid with earth torn from the mountainside,
and sweeping resistlessly along in its career a shower of stones and
rock-fragments. That which happens thus occasionally with many
streams is more or less the work all the year round of many more.

As the torrent grows less rapid, lower down in its course, it ceases to
carry rocks and stones, though the grinding and wearing away of stones
upon the rocky bed continues, and coarse gravel is borne still upon its
waters. Presently the widening stream, flowing yet more calmly, drops
upon its bed all such coarser gravel as is not worn away to fine earth,
but still bears on the lighter grains of sand. Next the slackening speed
makes even the sand too heavy a weight, and that in turn falls to line
the river-bed, while the now broad and placid stream carries only the
finer particles of mud suspended in its waters. Soon it reaches the ocean,
and the flow being there checked by the incoming ocean-tide, even the
mud can no longer be held up, and it also sinks slowly in the shallows
near the shore, forming sometimes broad mud-banks dangerous to the
mariner.
This is the case only with smaller rivers. Where the stream is stronger,
the mud-banks are often formed much farther out at sea; and more
often still the river-detritus is carried away and shed over the ocean-bed,
beyond the reach of our ken. The powerful rush of water in earth's
greater streams bears enormous masses of sand and mud each year