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heat and water into hydrogen, carbon, and oxygen, their primitive elements. Sometimes, however, vegetables, previous to this their final change, become petrified.

Petrifactions are not substances converted into stone, as many persons suppose: they are substances incrusted, for the most part, with carbonate of lime. Sir J. Mackenzie lately discovered a fossil Scotch pine-tree in the village of Pennicuik, about ten miles from Edinburgh, on the North Esk River. The strata in which the remains of this tree were found are slate clay, but the tree itself is incrusted with sandstone. There is sandstone both above and below the slate clay, but the roots of the tree do not appear to have penetrated the latter, though they reach down to it.

Whole forests, completely coated either with compact or shelly substances, are found on Kangaroo Island; also on the continent of New-Holland. These incrustations are supposed by M. Perron to arise from decompositions of shellfish, which, transported by the winds, are deposited on the trees and plants in the form of dust, and soon become solid pellicles around the branch on which they light. This causes the gradual decay of the tree, which, yielding to the influence of the calcareous matter, disorganizes, and, after no great length of time, becomes a mass of sandstone, the arborescent form of which alone recalls to the eye of the observer its former vegetable state.

GEOLOGICAL CHANGES.

It has been beautifully said by M. Necker, "The blissful idea of a GoD sweetens every moment of our time, and embellishes before us the path of life; unites us delightfully to all the beauties of Nature,

and associates us with everything that lives or moves." Thus we are led to contemplate Nature with satisfaction in all her attitudes.

The effects of volcanoes are generally known; it is not, therefore, my intention to enter into a history of them, though we may just note a few of comparatively recent occurrence. A great part of the Passandayang, in Java, was swallowed up in 1772 with explosions louder than the heaviest ordnance. Forty villages were destroyed; and 2957 inhabitants, and a strip of land fifteen miles in length by six in breadth, ingulfed. In 1776 the whole city of Cumana was overturned; and in a subsequent earthquake at Caraccas, nine tenths of that city were destroyed, and 10,000 persons buried in its ruins.

Earthquakes are frequent and fatal in Peru, where entire districts are devoted, as it were, to incessant volcanic action.

Volcanoes doubtless operate as safety valves, for the want of which in many places earthquakes have occurred. In 1600 a volcano in Peru covered an area of above thirty-four thousand square acres with sand, ashes, and other matter. Bouguer seems to think, that from the multitude of caverns and volcanoes found in them, the solidity of the Cordilleras by no means corresponds with their bulk. It is curious to observe, that while volcanoes spread such wide and incessant destruction in the southern, they are totally unknown in the northern parts of the American continent. Nor have any data yet been discovered which lead to the conclusion that there ever have been any.

Java, one of the finest islands in the world, is, on the contrary, almost entirely volcanic. Dr. Horsfield visited one of the craters. "Everything," says he, "contributes to fill the mind with the most awful satisfaction. It doubtless is one of the most grand and terrific scenes which Nature presents, and afforded an enjoyment which I have no power to de

scribe." In that island there was an eruption in 1586 which destroyed ten thousand persons. But a more extraordinary one was that of Tomboso, a mountain situated in the Island of Sambawa, in the year 1815. So extensive was this explosion, that its effects extended over the Molucca Islands, a large portion of Celebes, Sumatra, and Borneo, to a circumference of a thousand miles from its centre, by tremulous motions; and its reports were heard at Java (three hundred miles distant), and inspired as much awe as if the volcano had been there; while such showers of ashes fell upon the island as totally to darken the atmosphere. The ashes, too, lay an inch and a half deep at Macassar, distant two hundred and fifty miles. The sea was, for many miles round Sambawa, so covered with pumicestone and trunks of trees as to impede the progress of ships; and the atmosphere was for two entire days dark as the darkest night. The air was still, but the sea much agitated. The explosions were not only heard at Java and the before-mentioned islands, but at Banca and Amboyna: the latter 890 miles distant, the former 986.

In 1783 a volcanic eruption broke out in Iceland, and for two months spouted out volumes of matter to a height of two miles, covering in its fall a tract of land to the extent of three thousand six hundred miles square. In this island volcanoes have all the dreadful accompaniments of those in Italy, but few of their benefits. In Iceland they produce no fertility; but in Italy, the fertility they occasion atones in no small degree for the previous desolation.

If we recur to earthquakes, the scene of change widens to an astonishing extent. A high mountain in one of the Molucca Islands has been changed into a lake, of a shape answering to its base; St. Calphurnia, in Calabria, and all its inhabitants, were overwhelmed by one earthquake; while by another (A.D. 1692-3), not only fifty-four towns and cities,

besides villages, were damaged or destroyed, but sixty thousand persons perished.

Not more astonishing were the effects of the great earthquake at Lisbon than the extent of its operations. It was not only felt at Lisbon and Oporto; in every province of Spain except those of Valentia, Aragon, and Catalonia; at Algiers; in the kingdom of Fez; in the empire of Morocco; in the Madeira Islands, and in those of Antigua and Barbadoes in the western hemisphere, but also in Corsica; at Bayonne, Bordeaux, Angoulême, and Havre in France; in many parts of Germany, Bohemia, Switzerland, and Holland; England, Wales, Scotland, Ireland, and Norway.

That earthquakes are of volcanic origin there can now, I think, be very little doubt; the larger shocks being the consequences of the primary impulses, the causes of which have not yet been solved; and the minor ones the results of the undulations of the strata.

There is no science, if we except Astronomy, that awakens so magnificent a conception of the Divine Power as that of GEOLOGY.

The Pythagoreans derived the greatest consolation from the ever-changing aspect of material objects; nor is there a finer passage in all Ovid than that wherein he gives a history of the natural and moral philosophy of Pythagoras.

. Beattie also has a magnificent passage:

"Of chance or change, oh! let not man complain,
Else shall he never, never cease to wail.

For from the imperial dome, to where the swain
Rears his lone cottage in the silent dale,

All feel the force of fortune's fickle gale.

Art, empire, earth itself, to change are doom'd; Earthquakes have raised to heaven the humble vale; And gulfs the mountains' mighty mass entomb'd; And where the Atlantic rolls wide continents have bloom'd."

The sea now separates Britain from France; Sicily from Italy; Terra-del-Fuego from Patagonia ;

Sumatra from Malacca; Haman from Quantong; Ceylon from the Carnatic; and the Island of Madagascar from the Continent of Africa. It is more than probable that all these islands were separated from the mainland by some vast convulsion of Nature. Herodotus even conjectures that all Thessaly was anciently a lake; while Pallas conceives that, in remote times, the Crimea was an island, and that the Black Sea surrounded it.

Whether America was really separated from Asia, or whether the two continents actually joined, we can never know. But such a union would be no more extraordinary than that subsisting between Asia and Africa at the Isthmus of Suez. The points which mark the two hemispheres are flat, and the sea more inclined to shallowness than depth. Volcanic matter has been found on the shores of Behring's Straits; and it has, therefore, been reasonably conjectured that the two continents may have been formerly connected. Earthquakes are frequent in Kamtschatka; and some terrible visitation of that nature may have rent asunder the isthmus that united them.

That the sea once covered the earth is clearly established by bones of animals, petrified fishes, strata of shells, and beds of vegetables under those marine substances, having been found in many countries in situations much higher than the sea, and not unfrequently on the sides and even summits of mountains. Some mountains in Chili are formed entirely of shells, few of which are in a state of decomposition; and on the Descaheydo, one of the Andes, not much inferior to Chimborazo, are oysters and periwinkles, calcined and petrified.

Bivalve shells have been also found on Mount St. Julian in Valencia, enclosed in beds of gypsum, surrounded by detached pieces of slate; petrified marine substances in a mine of native mercury in a steep hill near San Felippe; and in a white crag of

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