silicified wood, chert, agate, jasper, porphyry, lava, and other substances imbedded. The silicified woods are particularly abundant.

Respecting the remaining islands, I possess no information that can be relied on, and it is much to be wished that some geologist, in imitation of what has been done by Humboldt on the American continent, and by Von Buch in the Canaries, would present us with a detailed account of the physical structure of the Antilles collectively considered.

The whole of the volcanic operations above-described appear to have taken place, geologically speaking, at a very recent epoch, for the calcareous beds with which these rocks are associated all belong to a period when the shells of the present ocean were already in existence.

Hence if, as Cortes observes, we figure to ourselves the condition of the Minor Antilles before the elevation of the coral rocks of which it principally consists, we shall find the whole Archipelago disappear, excepting a few primary rocks occasionally scattered about.

The volcanic islands are all placed in one series, forming an arc, connecting, by means of its two extremities, the primary mountain range of Porto Rico, St. Domingo, and Jamaica with the parallel chain of the Silla in the Caraccas, and the connexion between the latter and the volcanos of the Antilles was fully established in 1812, by the cessation of the earthquakes on the mainland so soon as the crater of St. Vincent showed symptoms of activity.

Thus if the parallel lines A stand for the primary range of the Larger Antilles; and those marked for the chain of the Caraccas; B will denote the position of the volcanic islands connecting both.

А

B

с

CHAPTER XXX.

VOLCANOS OF NORTH AMERICA, OR ABOVE THE ISTHMUS

OF DARIEN.

North and Central America—Oregon Territory.-California-Mexico

Guatemala.

No signs of volcanic action have been discovered in any part of the continent of North America above the tropic of Cancer, excepting to the west of that great dividing ridge, called the Rocky Mountains, which stretches in a direction north-west and south-east, from the Arctic Sea to the Isthmus of Panama.

This lofty system consists, so far as it has been yet examined, entirely of primary formations; but to the west, and nearly parallel to it, is a distinct group, called the Far West or Sierra Nevada range, which rises to a greater height even than the Rocky Mountains themselves; the pass which was crossed by Fremont* in one of his exploring expeditions, in lat. 38°•44, long. 120°:28, being no less than 9338 feet above the sea.

This latter chain runs very near to the coast with which it is parallel; and as the waters that accumulate in the great longitudinal valley intervening between it and the Rocky Mountains, can only find an outlet to the sea in the few spots where a gap occurs in the ridge, as for instance where the Columbia River flows into the Pacific, we can readily understand the paucity of large streams, as well as the existence of extensive lakes, some of which, as that of Utah, by reason of having no outlet, are salt or brackish.

Now volcanic phænomena appear to occur abundantly in many parts of this chain, as well as in the valley to the east of it.

Beginning as far north as latitude 60°, we find the Mount

* Fremont, Two Exploring Expeditions, 1846.

St. Elias, probably the loftiest eminence in the northern continent of America, being nearly 18,000 feet above the sea, which is stated to be an active volcano, and is perhaps connected with the chain of the Aleutian Islands already alluded to.

Mount Fairweather, Cerro de Buen Tiempo, a little to the south, is another volcano about 15,000 feet in height; and to the north, volcanic appearances have been found on the coasts of Prince William's Sound.

Another volcano, in lat. 57o.3, has been recognized by Captain Lisiansky; it is called Mount Edgecumbe, and consists of basaltic porphyry with crystals of felspar, whilst its flanks are covered with pitchstone and pumice. According to Ernest Hoffman its height is 2853 feet.

In lower latitudes the volcanic action seems either extinct or more languid. Near the Utah lake, in the 40th parallel, are the Beer Springs, thermal waters strongly impregnated with carbonic acid gas, and hence possessing the pungent taste from which their name is derived. The hottest, called Steamboat Spring, has a temperature of 85o. Scoriform

° basalt occurs in its vicinity, and not far from it is a perfect volcanic crater, 360 paces in circumference and sixty feet in depth, with every indication of recent fusion in the rocks of which it is composed.

Other thermal waters occur, associated with vesicular trap, in lat. 420.55, and cause a copious deposition of calcareous matter. Indeed, within the valley intervening between the two parallel chains of mountains, volcanic rocks and thermal springs abound between the 38th and 42nd parallel of latitude; and in one of the chain of lakes already noticed as existing in this valley, there rises a pyramidal mass of rock, probably volcanic, which has caused it to be distinguished by the name of the Pyramid Lake.

In the peninsula of Old California there is a chain of mountains forming the central ridge, and called Cerro de la Giganta (from 4592 to 4920 feet), which appears to be of volcanic origin; and one of them, the Monte de las Virgines, is said to be in a state of activity. It is to be regretted that we know as yet so little of the geology of this part of the continent.

a

In Mexico, the most northern point in which any signs of volcanic action are known to occur is near the town of Durango, in lat. 24°, long. 104°, where a group of rocks covered with scoriæ, and consisting of basaltic amygdaloid, called La Breña, rises in the midst of a level plain.

On the summit of one of the neighbouring mountains a regular crater was discovered, but no active volcanos are to be met with until we reach the parallel of the city of Mexico itself, where almost in the same line occur five, so placed that they appear to be derived from a fissure traversing Mexico from west to east, in a direction perpendicular to that of the great mountain chain, which, extending from north-west to south-east, constitutes the great table-land of the American continent. It is interesting to remark, that if the same parallel line which connects the active volcanos of Mexico be prolonged in a westerly direction, it would traverse the group of islands called the Isles of Revillagigedo, which there may be reason to consider volcanic from the pumice found amongst them *.

The most eastern of the above volcanos, that of Tuxtla, is situated a few miles to the north-west of Vera Cruz. It had a considerable eruption in 1793, the ashes from which were carried as far as Perote, a distance of fifty-seven leagues.

In the same province, but farther to the west, occur, the volcano of Orizaba, the height of which is 17,300 feet, and the Peak of Popocatepetl, 300 feet higher, the loftiest eminence in New Spain. The latter is continually burning t, though for several centuries it has thrown nothing up from the crater but smoke and ashes.

To the west of the city of Mexico are the volcanos of Jorullo and Colima. The elevation of the latter is estimated at about 9000 feet. It frequently throws up smoke and ashes, but has not been known to eject lava.

The volcano of Jorullo, situated between Colima and the town of Mexico, is of much more modern date than the rest, and the great catastrophe which attended its first appear

* See the map of Mexico which accompanies this volume.

+ Mr. Bullock has called in question this statement of Humboldt's ; but a still more recent traveller, Mr. Stapleton, has confirmed it (Bull. des Sci. for September 1825).

ance is perhaps (says Humboldt) one of the most extraordinary physical revolutions in the annals of the history of our planet*.

Geology, he remarks, points out parts of the ocean near the Azores, in the Egean Sea, and to the south of Iceland, where, at recent epochs, within the last 2000 years, small volcanic islands have risen above the surface of the water ; but it gives us no example of the for. mation, from the centre of a thousand burning cones, of a mountain of scoriæ and ashes 1695 feet in height, comparing it only with the level of the adjoining plains, in the interior of a continent, thirty-six leagues distant from the coast, and more than forty-two leagues from every other active volcano.

A vast plain extends from the hills of Aguasarco nearly to the villages of Teipa and Pelatlan, both equally celebrated for their fine plantations of cotton. Between the Picachos del Mortero, the Cerros de las Cuevas and de Cuiche, this plain is only from 2400 to 2600 feet above the level of the sea. In the middle of a tract of ground in which porphyry with a greenstone base predominates, basaltic cones appear, the summits of which are crowned with vegetation, and form a singular contrast with the aridity of the plain, which has been laid waste by volcanos.

Till the middle of the last century, fields covered with sugar-cane and indigo occupied the extent of ground between the two brooks called Cuitimba and San Pedro. They were bounded by basaltic mountains, the structure of which seems to indicate that all this country, at every remote period, had been already several times convulsed by volcanos. These fields, watered by artificial means, be. longed to the farm of Don Pedro di Jorullo, and were among the most fertile in the country.

In the month of June 1759 a subterraneous noise was heard. Hollow sounds of the most alarming nature were heard, accompanied by frequent earthquakes, which succeeded each other for from fifty to sixty days, to the great consternation of the inhabitants of the farm. From the beginning of September everything seemed to announce the complete re-establishment of tranquillity, when in the night of the 28th and 29th the horrible subterraneous noise recommenced. The affrighted Indians fled to the mountains of Aguasarco. A tract of ground from three to four square miles in extent rose up in the shape of a bladder. The bounds of this convulsion are still distinguishable from the fractured strata.

* Nouvelle Espagne, p. 248, fol. ed.