The constant agitation of the waters, and the declivity of the bottom, are no doubt the causes of this gradual and widely extended deposition. A soft mass of alluvial deposit, having its pores filled with water, and being subject to the vibrations of a superincumbent fluid, will yield to the pressure of that fluid on the side of the least resistance, that is, on the side toward the sea, and thus will be gradually extended more and more over the bottom. This will happen not only to the finer parts of the detritus, but even to the grosser, such as sand and gravel. For suppose that a body of gravel rests on a plane somewhat inclined, at the same time that it is covered with water to a considerable depth, that water being subject not only to moderate reciprocations, but also to such violent agitation as we see occasionally communicated to the waters of the ocean; the gravel, being rendered lighter by its immersion in the water, and on that account more moveable, will, when the undulations are considerable, be alternately heaved up and let down again. Now, at each time that it is heaved up, however small the space may be, it must be somewhat accelerated in its descent, and will hardly settle on the same point where it rested before. Thus it will gain a little ground at each undulation, and will slowly make its way towards the depths of the ocean, or to the lowest situation it can reach. This, as far as we may presume to follow a progress which is not the subject of immediate observation, is one of the great means by which loose materials of every kind are transported to a great distance, and spread out in beds at the bottom of the ocean. 370. The lighter parts are more easily carried to great distances, being actually suspended in the water, by which they are very gradually and slowly deposited. A remarkable proof of this is furnished from an observation made by Lord Mulgrave, in his voyage to the North Pole. In the latitude of 65° nearly, and about 250 miles distant from the nearest land, which was the coast of Norway, he sounded with a line of 688 fathoms, or 4098 feet; and the lead, when it struck the ground, sunk in a soft blue clay to the depth of ten feet.[186] The tenuity and fineness of the mud, which allowed the lead to sink so deep into it, must have resulted from a deposition of the lighter kinds of earth, which being suspended in the water, had been carried to a great distance, and were now without doubt forming a regular stratum at the bottom of the sea. [Footnote 186: Phipps's Voyage, p. 74, 141.]