Depth charge

“ These groups are (1) shallow-water deposits, made in water less than some such depth as 100 fathoms, and (2) deep-sea deposits, laid down in water of greater depth. The selection of the 100-fathom line as the dividing depth is less arbitrary than it seems, for passing outward from the shore, it is at about this depth that the bottom ceases to be commonly disturbed by the action of currents and waves; that sunlight and vegetable life cease to be important at the bottom ”

“ But the efficacy of the sea as a denuding agent, geologically considered, is not dependent on the power of currents to preserve at great depths a velocity sufficient to remove sand and mud, because, even where the deposition or removal of sediment is not in progress, the depth of water does not remain constant throughout geological time. ”

“ In a deeper stream such as that in fig. 130, the average height to which particles are lifted, and, since the rate of vertical fall through the water may be assumed the same as before, the average distance a′c′ of transport will be greater. Consequently, although the scouring action may be identical in the two streams, the velocity of transport of material down stream is greater as the depth of the stream is greater. The effect is that the deep stream excavates its bed more rapidly than the shallow stream. ”

“ Here the sinking of wells results in the finding of water at depths varying from twenty to forty feet, and boring to a greater depth would doubtless produce a fuller supply, for in so flat and porous a land, within easy measurable distance of the great inland sea, there is every probability that an inexhaustible supply is within touch. ”

“ From many of which kind of Experiments, it will likely not be hard to find out a method to calculate, what depth is to be concluded from any time of the like Globes stay under water: As for instance, if in the depth of 20 fathom, measured by the Line, the Globe stay under water 15 Seconds; then if the Ball stay 600 Seconds, the depth of the Sea is 933 fathom and 2 foot, if the Ball be found to move equal spaces in equal time. ”

“ As the pressure of water is nil at the surface and increases in direct proportion to the depth, the overturning moment is as the cube of the depth; and the only figure which has a moment of resistance due to gravity, varying also as the cube of its depth, is a triangle. ”

“ Few of us have not, at one time or another, looked down from a boat, to see golden sand, variegated pebbles, small fishes swimming about, at a considerable depth.
Thus with water, as with denser materials, transparency is merely a question of thickness. As the thickness increases, more and more rays of sunlight are taken captive, and the water becomes less and less translucent, till at length, if we could get deep enough, we should find ourselves to be surrounded with blackness.
Another feature of ocean-depths is that of immense pressure. ”

“ It is worth noting, however, that if a hole were dug into the crust of the earth to a depth of 15 or 20 miles the air at the bottom of the hole would be compressed by that above it to a density comparable with that of the solar gases. ”

“ If the bed of a lake or of the sea be sinking, whether at a uniform or an unequal rate, or oscillating in level during the deposition of sediment, these movements will give rise to a different class of phenomena, as, for example, to repeated alternations of shallow-water and deep-water deposits, each with peculiar organic remains, or to frequent repetitions of similar beds, formed at a uniform depth, and inclosing the same organic remains, and to other results too complicated and varied to admit of enumeration here. ”

“ This method of sounding answers very well for comparatively shallow water, but it is useless for depths much over 1,000 fathoms, or six thousand feet. The weight is not sufficient to carry the line rapidly and vertically to the bottom; and if a heavier weight is used, the ordinary sounding line is not strong enough to draw up its own weight, and that of the lead from a great depth, and so breaks. No impulse is felt when the lead touches the bottom, and so the line continues running out, and any attempt to stop it breaks it. ”

“ If we consider the rock as a mass completely saturated with water through a certain vertical depth, the water being in a state of equilibrium, when a well is sunk, and the water pumped up, the state of equilibrium is destroyed, and the water in the rock is forced in from all sides. ”

“ For suppose the globe to be evenly covered with sea, to a depth say of a thousand fathoms—then, whatever might be the mineral matter composing the sea-bottom, little or no deposit would be formed upon it, the abrading and denuding action of water, at such a depth, being exceedingly slight. ”

“ But if no foreign matter be introduced, the buildings, when once removed to a depth where the action of the waves is insensible, and where no great current happens to flow, may last for indefinite periods, and be as durable as the floor of the ocean itself, which may often be composed of the very same materials. ”

“ If, for example, marine strata, about the age of our chalk and greensand, have been lifted up in Europe to an extreme height of more than eleven thousand feet, and a mean elevation of some hundreds, we may conclude that certain parts of the surface, which existed when those strata were deposited, have sunk to an extreme depth of more than eleven thousand feet below their original level, and to a mean depth of more than a few hundreds. ”

“ The upper reaches of a river may present sufficient depth but too fast a current, or they may be too narrow, or the curves may be too rapid, or the obstruction of rocks too common, for any sort of navigation, although the depth of water be sufficient. ”

“ At a certain depth, estimated at about six miles, the weight of the crust becomes greater than the rocks can bear, and all cavities and pores in them must be completely closed by the enormous pressure which they sustain. ”

“ In the interior of the earth, where all knowledge of its chemical and mineralogical character fails, we are limited to as pure conjecture as in the remotest bodies that revolve round the sun. We can determine nothing with certainty regarding the depth at which the geological strata must be supposed to be in a state of softening or of liquid fusion, of the condition of fluids when heated under an enormous pressure, or of the law of the increase of density from the upper surface to the centre of the earth.”—Cosmos, vol. ”

“ Now then such as try for bituminous Turf, or such as search for the depth of a Marsh, or seek after a sandy bottom, drawing forth the earth with long borryers or Caugers, do find that by how much the deeper they go, so much the less, sulphur they find, and at the bottom none at all. ”

“ The oceans, on the average, are not more than three miles deep; spread evenly over the surface of the whole earth, their depth would be less than two miles, while the water in the rocks, if it could be added to the seas, would make the total depth seven miles or more. As we shall note hereafter, the processes of formation of strata tend to imprison water in the beds, which in time is returned to the earth's surface by the forces which operate within the crust. ”

“ The greatest depth of water at which soundings have been obtained, being between five and six miles, is deeper than the altitude of the highest mountain of which we have knowledge; and there may be cavities of far greater depth. Geological researches prove that at an early period of the history of the earth its surface was vastly more irregular than at the present time. Not only the mountains on the earth were higher, but the deepest valleys of ocean were far deeper. ”

“ One may form an idea of the great depth of water at the narrow outlet when it is borne in mind that this vast quantity, falling over a ledge of rock a mile wide, finds its way out of the huge rock tank through that narrow channel. ”

“ When we recollect that the depth of the ocean is supposed frequently to exceed three miles, and that currents run through different parts of that ocean at the rate of four miles an hour, and when at the same time we consider that some fine mud carried away from the mouths of rivers and from sea-beaches, where there is a heavy surf, as well as the impalpable powder showered down by volcanoes, may subside at the rate of only an inch per hour, we shall be prepared to find examples of the transportation of sediment over areas of indefinite extent. ”

“ In yet another way deep wells are of special significance, that is in regard to the light which they throw upon the subterranean temperature of the earth. Very recently the deepest well in the world was drilled near Fairmont, West Virginia, to a depth of 7,579 feet, in quest of oil or gas. ”

“ For example, suppose it now takes a year to deposit mud enough at the bottom of the sea, to make an inch of rocks, and if mud was deposited no faster in those remote ages, then the rocks would be as old as there are inches in the eight or nine miles depth to which the strata extends. ”

“ For thirty miles and more you have a continuous stretch of reef, which gives throughout a uniform yield per ton, and which has been proved to the depth of some hundred feet, and may—there is every reason to believe—go to unknown depths. ”

“ The depth in which they accumulate varies a good deal, viz. from 200 up to 2000 fathoms, but as a rule is less than 1000 fathoms, and it is believed that the most common situations are where the continental shores slope rather steeply into moderate depths of water. ”

“ Laborious and scientific men have been at the pains to calculate the gradual increase of some of these now proceeding deposits,—such as the Deltas, in course of formation at the mouth of the Nile, and at the gorges of the Ganges; and they find that the progress of the depth of increase is exceedingly small,—probably not more than a foot in many years. ”

“ It included not only measurement of depths, but also of the temperatures at different depths, the study of plankton or surface ocean life, and of life in the depths. I remember what a revolution it caused in one’s ideas. When I went to sea we were taught that there was enormous pressure at great depths, sufficient to prevent the existence of life, for in descending the sea water got heavier and heavier under pressure. It was held that at 2000 fathoms a man would bear on his body a weight equal to 20 locomotive engines each with a goods train loaded with pig iron. ”

“ As I sounded through the ice I could determine the shape of the bottom with greater accuracy than is possible in surveying harbors which do not freeze over, and I was surprised at its general regularity. In the deepest part there are several acres more level than almost any field which is exposed to the sun wind and plough. In one instance, on a line arbitrarily chosen, the depth did not vary more than one foot in thirty rods; and generally, near the middle, I could calculate the variation for each one hundred feet in any direction beforehand within three or four inches. ”

“ The cause of the Natation & submersion of Solids in the Water.I say then the Cause why some Sollid Bodyes descend to the Bottom of Water, is the excesse of their Gravity, above the Gravity of the Water; and on the contrary, the excess of the Waters Gravity above the Gravity of those, is the Cause that others do not descend, rather that they rise from the Bottom, and ascend to the Surface. ”

“ The effect of a torrent in deepening its bed will explain the mechanical agency of fluid-water, though this effect is infinitely increased, and sometimes almost entirely dependent, upon the solid matters which are carried down by it. An angular fragment of stone in the course of ages moved in the cavity of a rock makes a deep round excavation, and is worn itself into a spherical form. ”

“ The reasoning of this celebrated geologist appears to be founded upon the assumption that when water, in consequence of its specific gravity, once sinks below the bottom of a current where it is shallowest, there is no force of traction in fluids, nor any other power, which can draw this heavy water up again. ”

“ For it seems in appearance, that the Sollid in sinking continually, raiseth so much Water in Mass, as answers to the parts of its own Bulk submerged: whereupon it is impossible, that a Solid less grave in specie, than water, should wholly sink, as being unable to raise a weight greater than its own, and such would a Mass of water equall to its own Mass be. And likewise it seems necessary, that the graver Solids do go to the Bottom, as being of a Force more than sufficient for the raising a Masse of water, equall to its own, though inferiour in weight. ”

“ So that a river, if it can preserve a given amount of velocity flowing over the sea, may deposit no very large amount of mechanically suspended detritus in its course from the embouchure, where it is ultimately stopped. Still, however, though the deposit may not be so abundant as at first sight would appear probable, the constant accumulation of matter, however inconsiderable at any given time, must produce an appreciable effect during the lapse of ages.”—Sir Henry De la Beche’s Geological Researches, p. ”

“ If the rock be hard and without bedding-planes and joints, or if its layers be thick and its joints few, clear water will be much less effective. If the surface of the rock be rough, the mechanical action of a swift stream of clear water might still produce some effect on it; but if massive hard rock presents a smooth surface to a clear stream, the mechanical effect of even a swift current is slight. ”