The OCEANS

. The Ocean floor
The sea fill all the hollows of the earth's surface that lie below "sea-level" with the exception of a few landlocked depressions,such as the land surrounding the cassias sea the polders of holland, and Yh valley of the river Jordan.
Whereas the average height of the land above sea-level is 2,750 ft,the average depth of the oceans is 12,300 ft. The greatest depth of the ocean at present known is 36,960 ft (the Mariana Trench , south-west of the island of Guam). On a globe of 16 in. Diameter this deep abyss would only be shown by a scratch 1/100 in. Deep, showing that the mountain heights and ocean deep make very little difference to the spherical shape of the earth ; in fact,no more than the irregularities on the skin of an orange .
The ocean floor is often referred to as being composed of four parts:---
(a) The continental shelf, a shallow area surrounding the land masses and never more than 600 ft (100 fathoms) deep
The boundary of the continental shelf is known as the continental edge.
(b) The continental slopes, the steep slopes descending from the continental edge to the deep sea plains .
(c) The deep sea plains a monotonous undulating area usually more than two miles below sea-level and comprising the greater portion of the ocean floor .
In some places the oceanic plain plunges to great depths known as the ocean deeps.
(d) The ocean deeps , which are usually long. narrow, though-like depressions.