Page images
PDF
EPUB
[ocr errors]

referred, there are others very numerous impregnated with petroleum, and the minerals allied to it, as bitumen, naptha, asphaltum and pitch. These springs are found in all parts of the globe, but the most powerful yet known, are those on the river Irawadi, in the Birman Empire, there being five hundred and twenty wells in one locality, yielding annually 400,000 hogsheads of petroleum. On both sides of the island of Trinidad, fluid bitumen is seen to ooze up from the sea. Hm the island is a pitch lake about three miles in cigeumference. The asphaltum is sufficiently, hard to support heavy weights in cold and wet weather, but during warm weather it is nearly fluid. In some places it is covered by the soil, and large crops of tropical productions are raised upon it, so that it is difficult to ascertain the boundaries of the lake. Mr. Lyell supposes that the materials for the formation of this bitumen, have been borne down by the Oronoco into the sea; and, collected by eddies or other causes into particular regions, have been acted upon by submarine volcanic fires. The frequent occurrence of earthquakes, and other volcanic phenomena in the island, lends countenance to this opinion. In addition to those above mentioned, we may enumerate the saliferous or brine springs, which are everywhere so common over the globe. The agency of these springs, in the formation of rocks, is of less importance than that of the calcareous, or the silicious. . Often they are strong solutions of pure rock salt, or muriate of soda, and furnish large quantities of that valuable article for the purposes of domestic economy. Such are the salt springs in the neighborhood of Salina, and Syracuse, in the State of New York. At Salina, the well is seventy feet deep, and about 480 gallons of brine are raised in one minute, and Dr. Beck states that 434 gallons are required to yield a bushel of salt, weighing 56 lbs. The well at Syracuse 170 feet deep, the pumps raise 62 gallens per minute, and 46 gallons are required to make a bushel of salt. The water is clear and sparkling, and of a temperature of 50° (Fahr.) at Salina, and 51° at Syracuse. These salt springs are supposed to be owing to immense beds of rock salt, although no borings yet made, have reached these beds. The valleys of the Mississippi and the Ohio abound in salt springs, and are based almost wholly on the saliserous or salt bearing rocks. Two distinct strata of these salt rocks, known as the upper and lower salt rocks, are found on the Muskingum, about 400 feet apart. The stone itself is a white, or sometimes reddish tinted and poroussandstone, the upper, is 25 feet thick; and the lower 40, and this yields the strongest brine. At Cheshire England, are numerous brine springs, and the salt springs of Droitwitch, a small town in Worcestershire, are superior to any other in the island; they are supplied from beds of rock salt, or rather veins, lying below a bed of gypsum ; for a long time the salt was made only from the brine which penetrated this bed, but about a century ago it was bored through and a large salt river was found to flow below. The depth of the river of brine below the surface, is about 200 feet, 150 of which are gypsum ; the river flows over a bed of rock salt and is twenty-two inches deep. The origin of these extended deposits of salt has not yet been satisfactorily ascertained. The waters of the Dead Sea in Palestine, contain large quantities of muriatic salts, derived from entire rocks of this mineral, continually dissolving on its southern shore. The water contains forty-one parts in one-hundred of salt; a much greater proportion than that of the sea. It is impregnated also with other mineral substances, particularly bitumen, which floats upon its surface in such large quantities as would elsewhere sink. The volcanic appearance of the country, the almost perpendicular, black rock which bounds its eastern or Arabian side, and throws its black shadow over the dark waters, and the limestone and sandy cliffs on its western side, which tower up in fanciful shapes, lends countenance to the opinion that these mineral substances are the products of former volcanic action. We have now glanced at the most prominent effects of springs in modifying and changing the face of the globe; although the effect of any individual spring appears trifling, yet the aggregate of change either by disintegrating, or consolidating, is immense. We have already alluded to the transporting power of rivers. The small stream which is supplied by springs, and which flows for hundreds of miles with a power which seems scarcely sufficient to carry along a few sands, by continual accessions swells finally into an immense

SUBTerran Ean springs. 219

river, and when, from long continued rains, or from melting of snows and ice, the brooks and tributary streams are swollen, a flood of water is poured down to the ocean, which bears with it materials transported a thousand miles, and in quantities of which we can form little conception. The water, which falls upon the surface of the earth and penetrates its upper soil, and is thus protected from evaporation, descends lower and lower, until it meets some impervious bed of clay, or marl ; here it accumulates and forms a hidden pond, and slowly undermines whole tracts of

country, and in the course of ages subterranean rivers are formed.

The various mineral ingredients dissolved in water, are borne up by springs, and again flowing over or through the porous sands, form limestones, sandstones, and ironstones; and thus continually the process is going on. - The action of all springs, and running waters, is to level the surface of the earth. The streams, which always flow from an elevated source, bear down the disintegrated portions of mountains and hills, and tend continually to fill up the bed of the sea. Unless a counterbalancing cause existed, and the elevation was made to compensate this continual degradation or levelling, the whole dry land would ultimately disappear. We find in earthquakes and other volcanic effects the elevating power; and although, as we shall presently show, the sea may gradually encroach upon the shores of one country, yet the lands of another will be gradually upheaved, and something like a balance will be maintained. Minute therefore as are the transmutations which are going on continually around us, and by which, long since, in the same quiet manner, the leaf that floated down the stream, a thousand years ago, and the insect that dropped into water, have been incrusted, and preserved with a fidelity which mocks the sculptor's art, yet we see that processes like these, have

“Turned the ocean-bed to rock,
And changed its myriad living swarms
To the marble’s veined forms.”

“How marvellous” observes Sir Humphry Davy, “are those laws by which even the humblest types of organic existence are

[ocr errors]
[ocr errors]

preserved, though born amidst the sources of their destruction; and by which a species of immortality is given to generations, floating, as it were, like evanescent bubbles on a stream raised from the deepest caverns of the earth, and instantly losing what may be called its spirit in the atmosphere."

[merged small][ocr errors]

“Thy shores are empires, changed in all save thee — Assyria, Greece, Rome, Carthage, what are they Thy waters wasted them while they were free, And many a tyrant since ; their shores obey The stranger, slave, or savage; their decay Has dried up realms to deserts:—not so thou, Unchangeable, save to thy wild wave's play— Time writes no wrinkle on thine azure brow— ‘Such as Creation’s dawn beheld, thou rollest now !” Byron. WE are, now to consider the remaining aqueous causes of change, currents and tides. The joint action of these produce mutations of great geological interest. The tides, or the great tidal waves which flow over the surface of the ocean at stated intervals, are mainly caused by the attraction of the moon, and hence we may show, and by no very extended chain of causation, that the effect of the moon in altering and keeping in a state of perpetual mutation the face of the earth, is by no means inconsiderable. A more remote cause, the rotation of the earth upon its axis, produces in part at least, great currents which constantly flow in vast circuits in the Atlantic, Pacific, and Indian oceans. In addition to the circular currents which thus flow through the oceans which we have named, there are immense bodies of cold water continually moving from the polar regions towards the central portions of the earth, and, as these currents are exhibited superficially, or on the surface, bearing down immense fields of ice, and since the storms and fogs of those regions are not suffieient to supply this waste of the waters, we may infer that an under current of warmer water passes continually from the equatorial to the polar regions. The polar current of the southern regions seems to be more powerful than that of the northern. Ice

« PreviousContinue »