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as is true of that which separates in the decomposition of permanganates and chromates by oil of vitriol.* The plant, then, appears to be an agent of nitrification when living as well as when dead, and ozone is the result of a molecular change which accompanies the decomposition as well as the formation of oxygen compounds.

Sheffield Laboratory, Dec., 1868.

Art. XX.–Geological Notes on the Andes of Ecuador ; by

JAMES ORTON.

The Andes traverse the Republic of Ecuador in two Cordilleras, which are nearly parallel to each other and on the average, forty miles apart. The great valley which they enclose is about 300 miles in length, and has a general direction of 58' W. It is divided by two transversal dikes—the knots of Tiupullo and Assuay into three basins; Quito, Ambato, and Cuenca, having the respective altitudes of 9,500, 8,000 and 7,800 feet above the Pacific. There are some subordinate knots, and some longitudinal ridges ; but all the basins lie parallel to the axes of the Cordilleras—a characteristic feature of the Andes. There are deep valleys on the outside flanks, which are evidently valleys of erosion; but the basins enclosed by the Cordilleras were created with them.

We b-lieve with Darwin, that the Andes did not suddenly reach their present gigantic proportions. Wilson counted six terraces in going up from the sea, through the province of Esmeraldas toward Quito. Moreover, such an assemblage of great volcanoes, among them Cotopaxi, the highest open vent on the earth's surface, and Sangai, the most active in its eruptions, shows that the energy which heaved the Andes, is of deep seated origin, and that it is not yet expended. We are also reminded of the law that "volcanoes in a state of action, concur with proofs of recent elevation.” Above the terraces are the cerros, or outlying spurs ; and still higher are the paramos or bleak, grassy highlands, out of which rise the icy peaks. The west slope of the Ecuadorian Andes, is about 275 feet per mile ; on the east, it is 125.

The mountain chain is built up of granitic, gneissoid and schistose rocks, often in vertical position, and capped with

* May not the liberation of chlorine in preparing oxygen from a mixture of chlorate of potash and oxyd of manganese, be due to the action of ozone? Chlorine appears when the decomposition is effected in a low heat, but not when a high temperature is used. In the latter case ozone cannot exist.

trachyte and porphyry. Large masses of solid rock are rarely seen ; everything is cracked, calcined or triturated. While in Bolivia, the eastern Cordillera shows a succession of sharp, ragged peaks, in contrast with the conical summits of the Cordillera of the coast ; there is no such distinction in the Andes of the equator. The eastern Cordillera, has a greater mean height, and it displays more volcanic activity. Twenty volcanic mountains surround the great valley, of which twelve are in the oriental chain. Three of the twenty (Cotopaxi, Sangai and Pichincha,) are now active ; and five (Chiles, Imbabura, Guamani, Tunguragua and Quirotoa,) are known to have been active since the conquest. The truncated cone of Cotopaxi, the jagged, Alpine crest of ruined Caraguirazo, and

[blocks in formation]

10,000 ft.

Caraguirazo, looking west. the dome of Chimborazo, are the representative forms of the volcanic summits. Antisana and Cayambi, are fashioned after Chimborazo, though the latter is table topped rather than convex; Altar, Quirotoa, Iliniza, Sincholagua, Rumiñagui and Corazon, resemble Caraguirazo ; Tunguragua, Sangai, Llanganati

, Cotocachi, Chiles and Imbabura, imitate Cotopaxi ; Pichincha, Atacatzo and Guamani are irregular. The extinct volcanoes usually have double domes or peaks. This twin feature is prominent in other Andean volcanoes ; e. g., Illimani.

The growth of the cones since they began to erupt, is plainly exogenous. They rarely eject liquid lava, but chiefly water,* mud, ashes and fragments of trachyte and porphyry. From the deluges of water, result deep furrows in the sides ; and from the prevalence of the east wind, which is always met by the traveller on the crest of either Cordillera, there is a greater accumulation of ashes, and less snow on the west slope. In some of the craters, particularly of Pichincha, Altar and Rumiñagui, the western wall is lower than the eastern. Cotopaxi is exceptional, being lowest on the east side. there is no synchronism in the eruptions of Etna and Vesuvius, so there is no simultaneous activity of Cotopaxi and Pichincha. These volcanoes must have independent reservoirs, for Cotopaxi is 3,000 feet higher than Pichincha, and only

* Much of the water sent down from Cotopaxi, may be due to the melting of snow; but this cannot be true of Pichincha or Imbabura.

As

[blocks in formation]

10,000 ft.

Pichincha, looking west. thirty miles distant. It is generally believed by the natives, that Cotopaxi and Tunguragua, are sympathetic. The volcanoes of Ecuador, (excepting Sangai,) belong to Scrope's third order; "that in which eruptive paroxysms of intense energy alternate with lengthened periods of complete external inertness,-phase of prolonged intermittences.

Taking Cotopaxi as the center of the system of Ecuadorian mountains, we may arrange the lower peaks, on concentric orbits. On the first are Ruminagui and Sincholagua, 10 miles distant; on the second, Iliniza, Corazon, Atacatzo and Antisana, 25 miles ; on the third, Quirotoa, Pichincha and Guamani, 30 miles ; on the fourth, Langanati, 40 miles ; on the fifth, Tunguragua, Caraguirazo and Cayambi, 50 miles; on the sixth, Chimborazo, Imbabura, and Cotocachi, 60 miles ; on the seventh, Altar, 65 miles ; on the eighth, Sangai, 75 miles; on the ninth, Chiles and Assuay, 100 miles.

The chief dome of Chimborazo, presents from Guaranda a magnificent paraboloidal mass ; while from a spot near Riobamba, the profile of the whole mountain has the figure of a lion in repose. One fourth of the entire altitude is perpetually covered with snow. “ Chimborazo (said Humboldt,) is formed of one simultaneously uplifted mass of trachyte which has pierced, and reposes upon, secondary strata,” and Daubeny adds that “the trachyte dome was raised, and then the volcanic fire was shifted to another quarter.” But to us the upper third of the mountain appeared like a vast accumulation of volcanic matter ejected around and over a fissure in the upturned metamorphic rocks of the Cordillera. The rounded contour of the trachytic beds, as well as their porous texture, as Scrope contends, indicates their protrusion in an imperfect state of liquidity. We observed the following rocks on Chimborazo :* Fine-grained trachyte, gray, brown and dark colored (common.)

* In the volcanoes of the Galapagos Islands, the south wall is lowest; while the Mexican craters, are lowest on the northeast.

soft, reddish, Coarse, porphyroid trachyte, gray, Cellular trachyte, iron stained, Compact trachyte, gray,

(rare.) Fine-grained trachyte with seams of flint, Obsidian,

In the College of Riobamba are specimens of brown trachyte in quite regular trihedral prisms.

The crown of Pichincha presents three groups of rocky peaks. The most westerly one, called Rucu-Pichincha, alone manifests activity. It is the only volcano in Ecuador which has not a true cone crater. Some violent eruption beyond the reach of history, or tradition, has formed an enormous funnelshaped basin 2,500 feet deer, 1,500 feet in diameter at the bottom, and expanding upward to a width of more than half a mile.f The abyss is girt with a ragged wall of dark trachyte which rises on the inside, either vertically or at the angle of 50°. The outside of the cone (so-called) is inclined 30°, and like the inside is covered with fine volcanic debris, chiefly pumice. The height of the cone as compared with the whole height of the mountain is as 1 to 10; that of Vesuvius being 1 to 3, and Teneriffe, 1 to 22. Bouguer and LaCondamine in 1742, were the first to reach the brink of this crater ; Visse and Moreno in 1844, were the first to enter it. The descent is extremely perilous, but the traveller is rewarded with one of the most imposing sights in nature. The bottom of the crater is covered with huge blocks of porphyry and trachyte scattered about in wild confusion. West of the center rises the real cone of eruption, an irregular heap of stones about 250 feet high and containing numerous fumeroles. Moreno rightly says, all the vents are situated in this little cone. The present products are sulphur and plumose alum lining the fissures, and aqueous vapor, with a small percentage of carbonic and sulphurous gases. The temperature of the vapor just within the fumerole we found to be 184°, water boiling beside it at 189°•2. The gigantic wall which girdles this fiery mount, is not only lower on the west side, but a deep cleft leads down into the wilds of Esmeraldas. A year ago the column of smoke did not rise above the top of the crater, but the volcano has lately been showing signs of activity such as it has not exhibited since the last grand eruption of 1660. On the 19th of March, 1868, detonations were audible at Quito, five miles distant in a straight line; and three days after there were more thunderings, with a great column of vapor visible from Chillo, twelve miles to the east. These phenomena were accompanied by an unusual fall of rain. On the 16th of August, occurred the great earthquake, since which event Pichincha has not made any extraordinary display.* The solid products of Pichincha since the Spanish invasion have been chiefly pumice and ashes. The roads leading to Quito cut through hills of. pumice. On the plain of Iñaquito and in the valley of Esmeraldas are vast erratic blocks of trachyte, some containing twenty-five cubic yards, and having sharp angles, and in some cases a polished unstriated surface. M. Visse does not consider them to have been thrown out of Pichincha, as LaCondamine and tradition have judged. We dislike to disagree with this habile observateur. It is true, as he says, that they could not have come out of the present cone at a less angle than 45°, for they would have hit the sides of the high escarpment and rolled back again, while at a higher angle they would not have reached their present location. But they could be the fragments of the upper portion of the original trachytic cone blown into the air, at the great eruption which cleared out the enormous crater. The following rocks we observed within and around Pichincha : Pumice, (lapilli,)

* Complete series of the Rocks mentioned in this paper, are preserved in the Cabinets of the University of Rochester, and of Ingham University, LeRoy, N. Y. They were kindly identified by Dr. T. Sterry Hunt, F.R.S., the distinguished mineralogist of the Canada Survey.

+ Orizaba in Mexico, 2,000 feet higher than Pichincha, has a crater 6,000 feet wide, but only 500 feet deep. That of Kilauea is from 600 to 1,000 feet deep.

# The author made two attempts to reach the bottom of this crater, the second of 'which was successful, Oct. 22, 1867. We were two hours in descending, and three hours in our exit. Mr. Farrand, a photographer, was the only American who had preceded us.

(common.) Coarse-grained trachyte with augite crystals, Granular trachyte, grayish,

Fine granular trachyte, reddish, * The natives ascribe the earthquake of 1859 to Pichincha. + Used as building material in Quito.

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