See how the Niagara has cut its way through
layer after layer of solid rock. But what is
the Niagara, with all the fresh-water courses
of the world, by the side of the great currents
of ocean? And what is the pressure of fresh
water upon river beds, in comparison with
the pressure of ocean water upon the bottom of
the deep sea? It is not so great by contrast as
the gutters in the streets are to the cataract.
Then why have not the currents of the sea worn
its bottom away?  Simply because they are not
permitted to get down to it.

Suppose that the currents, which we see at
and near the surface of the ocean, were
permitted to extend all the way to the bottom, in
deep as well as shallow water, let us see what
the pressure and scouring force would be where
the sea is only three thousand fathoms deep—
for, in many places, the depth is even greater
than that. It is equal there, in round numbers,
of the pressure of six hundred atmospheres, or
of six hundred and forty-eight tons upon every
square foot of solid matter. The better to
to comprehend the amount of such a pressure, let
us imagine a column of water just one foot
square, where the sea is three thousand fathoms
deep, to be frozen from the top to the bottom,
and that we could then, with the aid of some
mighty magician, haul this shaft of ice up, and
stand it on one end for inspection and examination.
It would be eighteen thousand feet high;
the pressure on its pedestal would be more than
a million and a quarter of pounds; and if placed
on a ship of six hundred and forty-eight tons
burden, it would be heavy enough to sink her.
There are currents in the sea where it is three
thousand fathoms deep, and some of them run
with a velocity of four miles an hour, and more.
Every square foot of the earth's crust, at the
bottom of a four-knot current three thousand
fathoms deep, would have, in round numbers, no
less than half a million of such columns of water
daily dragging, rubbing, scouring, and chafing
over it, under a continuous pressure of six
hundred and forty-eight tons.

How frail yet how strong, how light yet how
firm, are the foundations of the sea! Its waves
cannot fret them, its currents cannot wear
them; for the bed of the deep sea is protected
from abrasion by a cushion of still and heavy
water.  There it lies—that beautiful arrangement
—spread put over the bottom of the deep,
and covering its foundations so that they may
not be worn.

There is a river in the ocean: in the severest
droughts it never fails, and in the mightiest
floods it never overflows; its banks and its
bottom are of cold water, while its current is of
warm. It takes its rise in the Gulf of Mexico,
and empties itself into Arctic seas. This mighty
river is the Gulf Stream; there is in the world
no other such majestic flow of waters. Its
current is more rapid than the Mississippi or
the Amazon, and its volume more than a thousand
times greater. Its waters, as far out
from the Gulf  as the Carolina coasts, are of
indigo blue. They are so distinctly marked
that their line of junction with the common
sea-water may be traced by the eye. Often
one-half of the vessel may be perceived floating
in gulf-stream water, while the other half is in
common water of the sea—so sharp is the line
and such the want of affinity between those
waters.

At the salt-works of France, and along the
shores of the Adriatic, where the " salines" are
carried on by the process of solar evaporation,
there is a series of vats or pools through which
the water is passed as it comes from the sea,
and is reduced to the briny state. The longer
it is exposed to evaporation, the salter it grows,
and the deeper is the hue of its blue, until
crystallisation is about to commence, when the
deep blue puts on a reddish tint. Now, the
water of the Gulf Stream is salter than the
shore water of the sea through which it flows,
and hence we can account for the deep indigo
blue which all navigators observe in Gulf Stream
water off the Carolina coasts. The salt-makers
are in the habit of judging of the richness of
sea-water in salt by its colour; the greener the
hue, the fresher the water. We have in this,
perhaps, an explanation of the contrasts which
the waters of the Gulf Stream present with
those of the Atlantic, as well as of the light
green of the North Sea and other Polar waters;
also of the dark blue of intertropical seas, and
especially of the Indian Ocean, which poets
have described as the " black" waters. What
is the cause of the Gulf Stream has always
puzzled philosophers. Many are the theories
and numerous the speculations that have been
advanced with regard to it. Late investigations
are beginning to throw some light upon the
subject, though all is not yet entirely clear.

Modern ingenuity has suggested a mode of
warming houses in winter. It is done by
means of hot water. The furnace and the
caldron are sometimes placed at a distance
from the apartments to be warmed. On reaching
their intended scene of action, the hot water
pipes are flared out, so as to present a large
cooling surface; after which, they are united
into one again, through which the water, being
now cooled, returns of its own accord to the
caldron. The cool water is returning and
flowing in at the bottom of the caldron all the
while that hot water is continually flowing out
at the top. Now, to compare small things with
great, we have, in the warm waters which are
contained in the Gulf of Mexico, just such a
heating apparatus for Great Britain, the North
Atlantic, and Western Europe.

The furnace is the torrid zone; the Mexican
Gulf and the Caribbean Sea are the caldrons;
the Gulf Stream is the conducting pipe. Such
an immense volume of heated water cannot fail
to carry with it beyond the seas a mild and moist
atmosphere. And this it is which so much
softens the climate of France and the British
Islands. Every west wind that blows, crosses
this stream on its way to Europe, and carries
with it a portion of this heat to temper there
the northern winds of winter. It is the influence