4 THE WORLD OF THE SEA. 
authority, affirms that the Atlantic has a mean depth of 550 
fathoms and the Pacific of 2,000 fathoms. Of course there are 
places in all seas unusually deep—the valleys and defiles in the 
ocean bed. The American, Lieutenant Walsh, in the Atlantic, 
off the shore of the United States, sounded the enormous depth 
of 5,640 fathoms. This is the deepest ocean valley yet discovered. 
The highest mountain in the world immersed in that watery abyss 
would not rear its summit above the waves. 
From actual measurement as well as from theoretical expecta- 
tion it appears that the Southern Ocean is the deepest. Professor 
Haughton, of Dublin, concluded, from the enormous volume of the 
tidal wave, that the waters which lie in the neighbourhood of 
the Antarctic Circle must have a depth of eight or ten miles, and 
this seems not improbable. The Baltic is the shallowest of all 
the seas, its depth not exceeding 108 fathoms. 
We may form some idea of the enormous quantity of water 
occupying the bed of the ocean, when we find that were the seas 
emptied, it would require the flow of all the rivers in the world 
for 40,000 years to refill them. The wezgft of this accumulation of 
water is 7755 of that of the globe. Every one knows that salt water 
is heavier than fresh. A ship laden in a river until the water all 
but laps over her gunwales will sail safely on the sea, the superior 
density of the water bearing her up. The specific gravity of fresh 
water to that of salt is as 1,000 is to 1,027. The heaviest water 
in the world is that which is supposed to cover the site of the Cities 
of the Plain, the Dead Sea; the weight of its water is to that of 
the ocean as 1,228 is to 1,027. 
The colour of pure water is d/uwe. To this fact we owe the 
beautiful tint of the sky over our heads, and the prevailing shade of 
the clear waters “under the firmament.” The waters of the sea, 
however, are not always blue. The proximity of land, their depth, 
the colour of the bottom, all affect the shade. Far out at sea the 
ocean may well be called c@ruleum mare, for there a plain of azure 
blue stretches away on every side until it blends imperceptibly with 
the sky at the horizon. Nearer the shore the blue tint assumes 
a greener shade, and this shade isless pure as the land is neared, 
for the erosion of the waves disturbs the mud at the bottom, besides 
mingling with their waters particles of the cliffs against which 
