These changes operate silently, continuously, and unperceived by the ordinary observer; but Nature does not limit herself always and everywhere to such peaceful agencies.  At times, and in certain places, she acts with startling abruptness and extraordinary violence.  Let the volcano and the earthquake attest the immensity of her power.  Let the earthquake tell how, within the memory of man, the whole coast-line of Chili, for 100 miles about Valparaiso, with the mighty chain of the Andes, was hoisted at one blow, and in a single night (November 19, 1822), from two to seven feet above its former level, leaving the beach below the old low-water mark high and dry.  One of the Andean peaks upheaved on this occasion was the colossal mass of Aconcagua, which overlooks Valparaiso, and measures nearly 24,000 feet in height.  On the same occasion, at least 10,000 square miles of country were estimated as having been upheaved; and the upheaval was not confined to the land, but extended far away to sea,—­which was proved by the soundings off Valparaiso and along the coast having been found considerably shallower than they were before the shock.

In the year 1819, in an earthquake in India, in the district of Cutch, bordering on the Indus, a tract of country more than fifty miles long and sixteen miles broad was suddenly raised ten feet above its former level.  The raised portion still stands up above the unraised, like a long perpendicular rampart, known by the name of Ullah Bund, or God’s Wall.

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With a similar fertility of illustration, Herschel sets before us the phenomena of volcanic eruptions and their extraordinary effects.

In a district of Mexico, between the two streams of the Cintimba and the San Pedro, on the 28th of September 1789, a whole tract of ground, from three to four miles in extent, surged up like a foam-bubble, or the swell of a wave, to a height of upwards of 500 feet.  Flames, lurid and crackling, broke forth over a surface of more than half a square league; and the earth, as if softened by heat, was seen to rise and sink like the rolling tide.  Vast chasms opened in the earth, into which the two rivers poured their waters headlong; reappearing afterwards at no great distance from a cluster of hornitos, or small volcanic cones, which sprang out of the mighty mud-torrent that gradually covered the entire plain.  Wonderful and awful as were these phenomena, they were surpassed by the sudden opening of a chasm which vomited forth fire, and red-hot stones and ashes, until they accumulated in a range of six large mountain masses,—­one of which, now known as the volcano of Jorullo, attains an altitude of 1690 feet above the ancient level.

In like manner Sir John proceeds to describe an eruption of Mount Tomboro, in the island of Sumbawa, the influence of which was felt to a distance of 1000 miles from its centre, in strange tremulous motions of the earth, and in the clash and clang of loud explosions.  He says that he had seen it computed that the quantity of ashes and lava ejected in the course of this tremendous eruption would have formed three mountains of the size of Mont Blanc.