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Our ideas of the real extent of Objects on the Earth's Surface
often erroneous.—True height of Mountains.--Depths of the Ocean.-Of Mines.-Of Volcanic Foci.- Eruptions of Mud containing Fish.-Volcanoes only in Secondary Formations.-- True Scale on which to view the Earth.Form of the Earth.—Newton's Demonstrations.—Gravity and Centrifugal Force.—False inferences drawn from Newton's Hypothesis.— True Primitive Creations.—Density of the Earth.- Reflexions arising from the Subject.-The Days of Creation.
On entering on a subject so extensive as the consideration of the entire Globe, and with the intention of first viewing it in a general way, before we proceed to the examination of its particular parts, our first object ought to be to attain the necessary elevation from whence this full and general view may be obtained.
Man, in his little sphere of action, on a minute portion of its surface, finds his ideas so confined, that he is constantly misled by them, in forming conceptions of objects, beyond common, every day observation. Thus, when traversing the stupendous Alpine regions of the earth, the mind of a stranger is overcome with the unusual appearances of things; and it is in such scenes that the geologist but too often forms erroneous notions of the " fracture and
“ ruin of the solid crust of the earth.”* In like manner, an idea of immensity is attached to the fathomless abysses of the great deep, or to the profound sources of volcanic fires. These objects, however, great as they may appear in the common scale of human comparison, almost vanish, when the larger and more correct scale, on which the whole Globe has been framed, is applied to them. The entire diameter of the earth is computed at about 8,000 miles. Now, the loftiest peak upon the earth's surface,t though it rises to the enormous elevation of upwards of twenty-six thousand feet, is but five such miles above the general surface of the ocean. In like manner, the greatest depths of the ocean sink into comparative insignificance, when this scale is applied to them. For although the actual measurement of these depths is, and ever must remain, beyond the reach of human art, yet we have the strongest reasons (almost amounting to certainty,) for supposing, from analogy, that the form and surface of the bed of the sea, have no greater variation from the general level, than those of the surface of the dry land ;* and, consequently, that while there may be depths in the ocean extending to four or five miles, by far the
*“ In the midst of such scenes, the Geologist feels his “ mind invigorated; the magnitude of the appearances be“ fore him extinguishes all the little and contracted notions “ he may have formed in his closet; and he learns that it “ is only by visiting and studying these stupendous works, “ that he can form an adequate conception of the great “ relations of the crust of the Globe, and of its mode of formation.”
Edinburgh Encyclopedia, Mineralogy. It has been well observed, that greatness is only a comparative quality. It is true, that Alpine scenery is well calculated to enlarge the mind, and to extinguish notions, formed on a more contracted view, of the earth's surface. But even this enlarged view becomes contracted in its turn, unless the earth be viewed
+ Dhawalageri, in Asia. Mont Blanc is not quite three miles above the same level. On taking the mean height of twenty-nine of the greatest elevations in the Old World, it is found to be only one mile and three quarters.
The mean height of an equal number in the New World is nearly two miles above the level of the sea.
* We find it a general rule, probably without any material exception, that where a country is low, and the shore flat, the neighbouring sea is shallow in about the same proportion. On the contrary, where a coast is mountainous, and the cliffs high and precipitous, there we find the sea of very considerable depth, and nearly of the same form under water, as above. We have this point ably illustrated in the survey of the German Ocean,
with sections of the depths, in six different lines, from the shores of Great Britain to those of Holland, Denmark, and Norway, by Mr. Stevenson, in 1820. We come to the same conclusion on a small, but generally correct scale, by considering any fresh-water lake, the shores of which present a variety of scenery. In all the Swiss lakes it is very striking; and in some, where the immediate shores are of great elevation, the bottom of the lake has not yet been found.
greater portions of it, as of the dry land, do not vary more than from a few hundred feet to half a mile, from positive smoothness. *
The greatest depths that have ever been reached by actual soundings, have seldom exceeded one mile. Captain Parry, however, in latitude 57 degrees 4 minutes North, longitude 24 degrees 34 minutes West, and about one hundred leagues from any land, found no bottom with the deep sea clamms, and a line of 1020 fathoms, or one mile and 280 yards, being more than a quarter of a mile deeper than was reached by Lord Mulgrave.
* In the course of some late experiments at sea, on board H. M. sloop Trinculo, Captain Booth, by order of the Lords of the Admiralty, in order to find soundings at unusual depths, Mr. Massey made use of several newly invented machines for this purpose.
He sunk a copper globe, capable of sustaining great pressure, with a line of 840 fathoms. The globe was enclosed in a strong net of cord, and was fixed close on the line, at about 40 fathoms from the lead. Neither globe nor lead returned to the surface; the globe had exploded, by the high pressure, and the line appeared as if blown off by an air-gun. A second globe was sunk, with a greater weight, and the same quantity of line, and it was enclosed in a still stronger netting, made of log-line, and not fixed so close to the line as in the former trial. In this instance, the lead returned, without having reached the bottom; but the globe had exploded, and the net was blown to pieces. These experiments proved, to the satisfaction of Mr. Massey and Captain Booth, the impossibility of counteracting the effects of high pressure offered at great depths in the sea.
Mr. Scoresby sounded in latitude 75 degrees 50 minutes North, longitude 5 degrees 50 minutes West, with 1058 fathoms; and in latitude 76 degrees 30 minutes North, longitude 4 degrees 48 minutes West, with 1200 fathoms of line, or one mile and 640 yards, in neither instance finding the bottom. This last is, probably, the greatest depth of soundings ever attempted.
The deepest mines that man has yet been able to form, do not reach, in perpendicular depth, much beyond two hundred fathoms, or not more than about a quarter of a mile. M. Humboldt saw, in 1803, a mine, in Mexico, which was to be sunk to the great depth of 1685 feet, or 280 fathoms, and which was to require twelve years for its completion, which, however, appeared very doubtful.
In viewing even volcanic action on the same great scale by which we have measured the mountains and the depths, we cannot consider these awful phenomena of burning mountains as more than superficial pustules on the mere skin of the earth. It is now pretty generally: understood, and acknowledged, that water is one of the most active agents in the production of yolcanic fires; and when we consider the number of volcanoes in the interior of our continents, which have, to all appearance, become extinct from the want of that communication with the