Although the pressure at the bottom of the ocean must be tremendous, yet so incompressible is water that a cubic foot of it weighs but little more at the bottom of the sea than it does at the top. Thus a body which sinks will in time reach the bottom no matter what the depth may be. At a depth of two miles the pressure is over 300 times as much as at the surface of the water and here, as we have already found, it is about 15 pounds to the square inch.
If a bag of air which had a volume of 300 cubic inches at the surface were sunk in the ocean to a depth of two miles, it would have a volume of less than a cubic inch, and the pressure upon it would be several tons. It thus happens that deep sea fishes when brought to the surface have the air in their swimming bladders so expanded that the bladder is often blown out of their mouths.
129.Condition of the Ocean Floor. -The ocean floor is a vast, monotonous, nearly level expanse whose dreary, slimy and almost life- less surface is enveloped in neverending night and is pressed upon by a vast weight of stagnant, frigid water. Here and there volcanoes rise upon it with gradually sloping, featureless cones, and sometimes a broad wavelike swell reaches within a mile or so of the surface. Such a swell extends along the center of the Atlantic Ocean through Ascension Island and the Azores.
CRINOID.
There are no hills and vales, no mountain ranges having sharp peaks and deep valleys.
Gradually rising ridges and volcanoes, sometimes topped with coral islands, alone vary the monotony. It is the nether world of gloom and unaltering sameness. Here the derelicts of ages past, after their fierce buffeting with wind and wave, have found a quiet, changeless haven where they may lie undisturbed until absorbedAn animal now found only at considerable depths in the ocean.
into the substance of the all-enfolding
water. Some animal species which lived
in the light of former geological ages have here found a resting place where the strife of progress is stilled and the laggard in the race of development may live in peace.
130.The Carpet of the Ocean Floor. -Near the shore, the floorof the ocean is covered with sand and mud derived from the waste of the land. In the deeper sea the covering is a fine-textured material of animal origin called ooze. It is composed of the shells of minute ani- mals that live near the surface. The most abundant shell is that of a minute animal called the globigerina, hence the deposit is often called the globigerina ooze.
At a depth of about 3000 fathoms (18,000 feet) these shellsdisappear and a reddish clay appears. This clay is believed to be due to meteoric and volcanic dust and to the insoluble parts that remainGLOBIGERINA. (Greatly magnified.)
131.Waves.
after the calcareous (limelike) material of the minute shells has been dissolved in sinking through the deep water. No layers of this kind have ever been found on the land, and this is one of the reasons for believing that the depths of the sea have never been elevated into dry land, but that what is now deep ocean has throughout all time been deep ocean.
Experiment 124. -Take a long flexible rubber band or tube and having fastened one end, stretch it somewhat. Now strike down on it near one end with a small stick. A wavelike motion will be seen to travel from end to end of the band. It is evident that the particles of rubber do not enter into the lateral movement, but that they simply move up and down, whereas the wave movement proceeds along the band. A piece of paper folded and placed lightly upon the band will move up and down but not along the band. Thus wave motion does not necessitate lateral movement of the particles taking part in the wave.
When the wind blows over water, it throws the surface into motion and produces waves. The highest part of the wave is called the crest and the lowest part the trough. Trough and crest move along rapidly over the surface of the water. The particles of the water themselves, however, move somewhat like those in the rubber band. That the water itself does not move with the wave can be seen when a floating bottle is observed. It moves up and down but does not move forward. If the water moved along with the waves, it would be next to impossible to propel a boat against the direction of the wave movement.
That it is possible to generate wave movement without the particles themselves moving along with the wave is seen when a field of grain is bending before a gentle wind. The troughs and crests move one after the other across the field but the heads of grain simply vibrate backand forth. The crest of a water wave, however, is often blown forward by the wind and thus a drift in the direction of the wind is established at the surface.
When great waves are raised by the wind at sea, there is danger that theOCEAN WAVES.
mighty crests may be blown forward and engulf a ship. To calm the waves ships sometimes pour "oil on the troubled waters." The oil spreads out in a thin film over the water and forms a "slick" which prevents the wind from getting sufficient hold upon the water to topple over the crests, and thus the danger of being swamped is averted. It has been found that oil will spread out even in the direction of the severest wind.
Although sometimes waves are spoken of as "mountain high," it rarely happens that the height from trough to crest is over 50 ft. The length of these great ocean waves, or the distance from crest to crest or from trough to trough varies from 300 to 1500 ft. or more. The velocity is sometimes as great as 60 miles per hour, but usually not more than half of this. The movement of the waves stirs up the water and enables it to absorb the air which is so necessary for the existence of water animals.