In a general point of view, the surface of the earth may properly
be considered as one vast ocean, in which are placed a great
number of islands, whose sizes are various. Two of these islands are
called CONTINENTS;—because it has hitherto been impossible to sail
round them, owing to the frozen state of the waters of the Arctic
seas. That which has been for the longer space of time inhabited by
civilized nations, is called the eastern, or old continent, and contains
Asia, Europe, and Africa. The other comprises America, and is
named the western, or new continent. New Holland, a large tract of
land situated in the midst of the most extensive mass of waters, is
by some called a continent; but it is more proper to consider it as
the largest island in existence. An island differs from a continent only
in size, and the name continent is given to certain extensive portions
of land, for the sake of convenience in geographical descriptions.
The bottom of the basin of the ocean has irregularities, similar to
those seen on the surface of the land; and, if the waters were dried
up, would present to view, mountains, valleys, and plains. Islands
are therefore, the flattened tops of mountains, situated in the midst
of the sea. Immense masses of rocks are found in many places
under the water, and often rise so near the surface, that they are
dangerous to navigation. Near Marseilles, there is a quarry under the
sea, from which marble is obtained. These facts prove that the sea is
not bottomless, as some people suppose, although there are some
places so deep that no bottom has yet been found. It has been
supposed, by many geographers, that the depth of the abysses of
the ocean, are equal to the heights of mountains on land, and
therefore that the ocean is in no place more than thirty thousand
feet deep. The greatest depth that has ever been measured without
finding bottom, is four thousand six hundred and eighty feet.
The chief characteristic of the ocean, is the saltness of its waters,
which renders them disagreeable to the taste, and unfit for the use
of man. Thus mariners are often, although surrounded by water, in
danger of perishing from thirst, when their supply of fresh water has
been exhausted, while they are yet at a great distance from land.
The cause of this saltness is not yet ascertained. It is supposed that