This diagram will give a general idea of the relative depth, position and motion of the denser and of the lighter waters of the globe, as they would appear if the waters of the earth equally covered the whole surface, without the interruptions of the continents and islands. It supposes the solid globe to be split in two in the middle, through each of the poles, and the interior split surface presented to the spectator, with the depth of the ocean greatly magnified in its proportions.

I. The interior circle represents the solid globe.

II. The exterior ring represents the magnified depth of the waters of the ocean; the shaded por tions, the depth of the denser waters, or those at 39 degrees of temperature, with their northern and southern encircling apexes or zones of greatest depth at about 56 deg. north and south latitude; and their two polar concave axes, one at either pole.

III. The lighter portions of this outer ring represent the depth of the lighter surface waters of the ocean, which are above 39 degrees of temperature toward the equator, and below it, toward the poles: the one made light by heat, the other by cold. The four spheroidal concaves near either pole represent the depth of the fight and frozen waters, or ice, that lies immediately over and around the circle, or pole, of ext reme cold, 16 degrees from the geographical poles of the earth.

IV. The arrow heads show the general motion or movement of the waters, as they slide down, north and south, from the tops of these ridges or zones of dense waters, at 56 degrees latitude, toward the bottom of the sea, and force their return surface currents back again toward the same parallels. A glance at any good map will show how these currents must be varied by the shape of the continents and shoal waters. SEE WARREN'S PHYSICAL GEOGRAPHY; chart OCEANIC CURRENTS.

APPENDIX.

THE OCEANIC AVALANCHE AND ITS COUNTER

CURRENTS.

A Discourse delivered before the Illinois Natural History Society, at their annual meeting, June 24, 1862,

By J. B. TURNER.

[Copy-right secured. ]

I have, on a former occasion before this Society, spoken of SPIRIT, FORCE and MATTER, as the ultimate basis, occasion, and cause of all known phenomena, and of their differences, modes and functions.

The great material field, or theatre, through which these principally manifest themselves to us, is in like manner three-fold, namely, EARTH, air, and sea.

I design to call your attention this evening, by request of friends of the Society, to one of the great moving causes of these manifestations, which, it seems to me, our books and our philosophers have most strangely and unaccountably overlooked, even to the present hour.

I refer to what I shall venture to call the GREAT WATER SLIDE or AVALANCHE OF THE OCEAN, for want of a better name; though I am aware that the term AVALANCHE refers only to the slide of snow or crystalized water on the continental mountain heights. I now use the term to designate the slide of UNcrystalized water down the great steeps of the "dread unfathomable seas;" a phenomena more simple, terrible and sublime in its causes and effects, than any other, of which I am aware, in the whole created world, unless indeed we except the great law of gravity, which wheels and controls all worlds and spheres, and of which this PERPETUAL AvaLANCHE OF THE OCEAN is one of the most striking, majestic, and benign manifestations, that our planet affords: at once by its gran

deur over-awing all our philosophies; by its beneficence contributing to all our industries and arts; nurturing the very bones in our bodies as well as the fish of the great deep, and all the cattle and forests upon our thousand hills; still, so simple in all its means and ends, that when we confront it, its very simplicity is even more astounding than its vast reach and grandeur and power.

Of course in a single lecture, even if prolonged through a whole week, I could give you only a most meagre and bare-bone skeleton of this great ever-living, all-controlling POWER OF THE SEAS, and the lands. But I will console myself with the reflection that a "word to the wise is sufficient," and that the few hints which I may here suggest, will be followed up by more thorough and extensive investigations and elucidations, in abler hands.

But where shall I begin to describe the sublime harmony of FARTH, AIR, and SEA, as tuned to an everlasting concord by this great perpetual avalanche of the ocean? I am always confounded when I think of it, and know not where to begin or end, or what from the endless round of its great truths, first or last, to select or present. But I will begin with the simplest ultimate idea-the moving cause of all else the peculiar action of that mode of force which we call the force of heat, upon water.

It is well known to all, that the specific gravity of pure water is greatest at about the temperature of 3910, and that unlike most other substances, it becomes lighter at all temperatures above and below this temperature; while the intermixture of all saline or foreign substances somewhat varies this result.

This simple fact produces an irregular spheroidal plane or line of maximum density of the waters over the whole ocean, well known to philosophers and navigators, which culminates in two great belts or zones, or so to speak, mountain heights of the denser waters, piled around the whole globe between 50 ard 60° north and south latitude. These encircling zones, or oceanic mountain. heights, of these denser waters of the seas in each of the hemispheres, are perpetually sliding down, both towards the poles and equator, into the ocean depths below, by the simple power of gravity, while they are as perpetually replenished by the return currents on the surface, both from the north and the south, from the equator and from the poles. [See Diagram and Notes.]

This simple and sublime arrangement absolutely necessitates the constant agitation, a literal churning, as it were, of the whole ocean, by day and by night, from its lowest depths; and equally necessitates those vast currents and whirlpools on its surface, so well known to all, as well as a great open sea at either pole: thus not only keeping the sea pure and free from stagnation, for the safety of its own peculiar forms of life, but equalizing or mitigating all climates, enriching all lands, replenishing all soils, and ministering to the sustenance and support of all vegetables and all animals, on all continents and islands.