QUITO.

Nevertheless the frequent occurrence of earthquakes in the intermediate country renders it probable, that no natural separation exists between the two provinces, but that the same operations are in fact proceeding throughout the whole intermediate tract.

It appears probable, says Humboldt, that the higher part of the kingdom of Quito, and the neighbouring Cordilleras, far from being a groupe of distinct volcanos, constitute a single swollen mass, an immense volcanic wall, stretching from south to north, the crest of which exhibits a surface of more than 600 square leagues. Cotopaxi, Tunguragua, Antisana, and Pichinca, are placed on this immense vault, and are to be considered rather as the different summits of one and the same volcanic mass, than as distinct mountains. The fire finds a vent sometimes from one, sometimes from another of these apertures. The obstructed craters appear to us to be extinguished volcanos; but we may presume, that, since Cotopaxi and Tunguragua have only one or two eruptions in the course of a century, the fire is not less continually active under the town of Quito, under Pichincha, and Imbaburu.*

In Chili no less than sixteen volcanos are said to be in a state of activity. They are all situated near the middle of the range of mountains, which runs in a direction nearly parallel to the coast. The lava and ashes discharged from them never extend beyond the limits of the Andes.

Only two volcanos are found among the maritime and midland mountains: one at the mouth of the River Rapel, which is small, and emits only a little smoke at intervals; the other, the great volcano of Villarica, distinguishable at the distance of 150 miles, and said to be connected at its base with the Andes.

* Personal Narrative, vol. 4. p. 29, Eng. Tr

CHILI.

It continues burning without intermission, but its eruptions have seldom been violent. The base is covered with forests, and its sides with a lively verdure, but its summit reaches above the line of perpetual snow.

The most remarkable eruption of the Chilian volcanos was that of Peteroa, on the 3d of December, 1760, when the volcanic matter opened for itself a new crater, and a mountain in its vicinity experienced a rent several miles in extent. A large portion of the mountain fell into the Lontue, and having filled its bed, gave rise to a lake in consequence of the accumulation of the water.*

Thus a line of volcanic mountains may be traced at intervals from the 5th to the 40th degree of south latitude, running nearly parallel to each other; whilst the intervening spaces exhibit, in the frequent earthquakes that occur, phanomena of an analogous kind.

This apparent communication, or at least similarity of constitution, subsisting between the several parts of this tract, is the more remarkable, from the absence of all indications of volcanic action from the countries situated on the eastern side of the Andes, whether in Buenos Ayres, Brazil, Guyana, the coast of Venezuela, or the United States.

It is true there exist a little to the east of the Andes three small volcanos, situated near the sources of the Caqueta, the Napo, and the Morona, but these, in Humboldt's opinion, must be attributed to the lateral action of the volcanos of Columbia.

There is one remarkable phænomenon belonging to volcanos of the New World, which, though not altogether peculiar to them, is more frequent there than among those of Europe.

It often happens, that instead of ejections of lava proceeding from the volcano during its periods of activity,

*Molina. Hist. Natur. de Chili.

GENERAL REMARKS.

streams of boiling water mixed with mud alone are thrown

out.

It was once imagined that the mud and water were genuine products of the volcano, derived from some spot in the interior of the mountain, equally deep-seated with that from which the lava itself proceeds; but a fact recorded by Humboldt has done much to dispel this illusion.

It seems, that with this mud are often thrown out multitudes of small fish (Pymelodes Cyclopum), sometimes indeed in numbers sufficient to taint the air. Now as there is no doubt that these fish proceeded from the mountain itself, we must conclude, that it contains in its interior large lakes suited for the abode of these animals, and therefore in ordinary seasons out of the immediate influence of the volcanic action.

Admitting the existence of these lakes, it is certainly most natural, to attribute the water thrown out to the bursting of one of them, and the mud to the intermixture of the water with the ashes at the same time ejected.

The conclusions to which Humboldt has arrived from his observations on the physical structure of America, some of which have appeared, but the greater part remain unpublished, are as follows:

All the most elevated points of the Cordilleras are of trachyte, which rock encircles in zones a large portion of the table land, but rarely extends towards the plains. When the trachyte does not exist in sufficient quantity to cover the entire soil, it is scattered in small distinct masses on the back and crest of the Andes, raised in the form of pointed rocks from the bosom of the primitive and transition formations.

Trachytes and basalt are rarely found together, and there seems to be a mutual repulsion between these two classes of

GENERAL REMARKS.

formations. True basalts with olivine do not constitute beds interstratified with the trachyte, but when they are found near the latter, they are superposed.

These and other volcanic formations, such as clinkstone, amygdaloid, and pumiceous conglomerates, are the principal rocks met with above the trachyte; sometimes, however, small local. formations of tertiary limestone and gypsum

occur.

The circumstance however which deserves to be con sidered with the greatest attention, as leading to the most important consequences, is the apparent passage from the trachyte into the porphyry beneath it.

This rock, which Humboldt considers as belonging to the transition series, is distinguished from the porphyries which are most common in the Old World, by the almost entire absence of quartz, the presence of hornblende, of glassy as well as common felspar, and sometimes of augite. It would therefore be difficult to fix upon any absolute line of separa tion between this kind of porphyry and trachyte; it is only from the union of all these mineralogical characters with the presence of obsidian, pearlstone, and scoriform masses, and from the relative position of the rock, that we can deter mine it to be trachyte.

It is also equally difficult to pronounce where the trachyte begins, and the porphyry which supports it terminates, for glassy felspar gradually becomes more and more common as we ascend to the upper strata of the transition porphyry, and beds even occur in it, which are considered almost as characteristic of the trachytic formation.

Thus between the porphyries which contain the rich silver mines of Real del Monte, and the white trachytes with pearlstone and obsidian which compose the Mountain of Couteaux east of Mexico, an intermediate class of rocks

* This remark must be taken with very many exceptions, as Humboldt seems to allow. Gissement des Roches, p. 349.

GENERAL REMARKS.

occurs, which partakes sometimes of the characters of the older, and sometimes of the newer formation.

In South America likewise, the same remark applies to the strata intervening between the transition porphyry covered with black granular limestone, and the pumiceous trachytes constituting the active volcano of Puracè.

In like manner, in the very midst of the Mexican porphyry, so rich in gold and silver, we observe beds, destitute of hornblende, but abounding in long narrow crystals of glassy felspar, which cannot be distinguished from the clink-stone porphyry of Bilin, in the trachytic district of Bohemia. -In short Humboldt considers, that there is no more reason for admitting a natural line of separation between the transition and the volcanic formation of America, than there is between the former, and the secondary limestones which are found above it in the Old World.

Before however we proceed to draw any inferences from these observations, I would remind you of what I have said with respect to the parallel case of the porphyries of Hun ́gary, and would observe moreover on the present subject, that the authority justly due in general to the opinions of an individual so distinguished as Humboldt is in some degree weakened here by the circumstance of their being founded on observations made more than twenty years ago, at a time when the very existence of several of the rocks, to - which reference is repeatedly made, was unknown. It is therefore possible, not only that the observations of this philosopher, whilst in America, may have been deficient in that precision which the present improved state of the science would have imparted to them; but that his attempts to reconcile the facts themselves to systems since established, being made since his return, may not always have been successful.

When for instance Mons. de Humboldt speaks of the Muschelkalk, the Quadersandstein, and the Tertiary rocks