tations of volcanic activity here indicated, different as they are, applicable in this case? and have the linear accumulations of rock-detritus been upheaved upon fissures in the spots where they now lie (at the foot and in the vicinity of a volcano)? The two dykes of fragments, in this so slightly inclined plateau, called Volcan de la Hacienda and Yana Volcan, which I once considered, although only conjecturally, as cooled lava-streams, now appear to me, as far as I can remember, to present but little in support of the latter opinion. In the Volcan de Ansango, where the line of fragments may be traced without interruption, like a river-bed, to the pumice margins of two small lakes, the fall, or difference of level between Pinantura 1482 toises (9476 feet), and Lecheyacu 1900 toises (12,150 feet), in a distance of about 7700 toises (49,239 feet), by no means contradicts what we now believe we know of the small average angles of inclination of lava-streams. From the difference of level of 418 toises (2674 feet), there is an inclination of 3° 6'. A partial elevation of the soil in the middle of the floor of the valley would not appear to be any hindrance, because the back swell of fluid masses impelled up valleys has been observed elsewhere, for example, in the eruption of Scaptar Jökul in Iceland, in 1783 (Naumann, Geognosie, Bd. i, s. 160).

The word lava indicates no peculiar mineral composition of the rock; and when Leopold von Buch says that everything is lava that flows in the volcano and attains new positions by its fluidity, I add that that which has not again become fluid, but is contained in the interior of a volcanic cone, may change its position. Even in the first description 25 of my attempt to ascend the summit of Chimborazo (only published in 1837, in Schumacher's Astronomische Jahrbuch), I expressed this opinion in speaking of the remarkable "fragments of augitic porphyry which I collected on the 23rd June, 1802, in loose pieces of from twelve to fourteen inches in diameter, upon the narrow ridge of rock leading to the summit at an elevation of 19,000 feet. They had small, shining cells, and were porous and of a red colour. The blackest of them are sometimes light like pumice-stone, and as though freshly altered by fire. They 25 Humboldt, Kleinere Schriften, Bd. i, s. 161.

have not, however, flowed out in streams like lava, but have probably been expelled at fissures on the declivity of the previously upheaved, bell-shaped mountain." This genetic explanation might find abundant support in the assumptions of Boussingault, who regards the volcanic cones themselves "as an accumulation of angular trachytic fragments, upheaved in a solid condition, and heaped up without any order. As after the upheaval the broken rocky masses occupy a greater space than before they were shattered, great cavities remain amongst them, movement being produced by pressure and shock (the action of the volcanic vapour-force being abstracted)." I am far from doubting the partial occurrence of such fragments and cavities, which become filled with water in the Nevados, although the beautiful, regular, and, for the most part, perfectly perpendicular trachytic columns of the Pico de los Ladrillos, and Tablahuma on Pichincha, and, above all, over the small basin Yana-Cocha on Chimborazo, appear to me to have been formed on the spot. My old and valued friend, Boussingault, whose chemico-geognostic and meteorological opinions I am always ready to adopt, regards what is called the Volcan de Ansango, and what now appears to me as an eruption of fragments from two small lateral craters (on the western Antisana, below Chussulongo) as upheavals of blocks 26 upon long fissures. As

26"We differ entirely with regard to the pretended stream of Antisana towards Pinantura. I regard this stream (coulée) as a recent upheaval analogous to those of Calpi (Yana Urcu), Pisque, and Jorullo. The trachytic fragments have acquired a greater thickness towards the middle of the stream. Their stratum is thicker towards Pinantura than at points nearer Antisana. The fragmentary condition is an effect of local upheaval, and in the Cordillera of the Andes earthquakes may often be produced by heaping up" (letter from M. Boussingault, dated August, 1834). See page 270. In the description of his ascent of Chimborazo (December, 1831), Boussingault says: "The mass of the mountain consists, in my opinion, of a heap of trachytic ruins piled up on each other without any order. These trachytic fragments of a volcano, which are often of enormous size, are upheaved in the solid state; their edges are sharp, and nothing indicates that they had been in a fused or even a softened condition. Nowhere, on any of the equatorial volcanoes, do we observe anything that would allow us to infer a lava-stream. Nothing has ever been thrown out from these craters except masses of mud, elastic fluids and ignited, more or less scorified trachytic blocks, which have frequently been scattered to considerable distances" (Humboldt, Kleinere Schriften,

he has acutely investigated this region 30 years after myself, he insists upon the analogy which appears to him to be presented by the geognostic relations of the eruption of Ansango to Antisana, and those of Yana Urcu (of which I made a particular plan) to Chimborazo. I was the less inclined to believe in a direct upheaval upon fissures throughout the entire linear extent of the tract of fragments at Ansango, because this, as I have already repeatedly mentioned, leads at its upper extremity, to the two chasms now filled with water. Non-fragmentary, wall-like upheavals of great length and uniform direction, are however not unknown to me, as I have seen and described them in our hemisphere, in Chinese Mongolia, in granite banks with a floetz-like bedding 27.

Antisana had an eruption 28 in the year 1580, and another in the beginning of the last century, probably in 1728. Near the summit, on the north-north-east side, we observe a black mass of rock, upon which even freshly fallen snow does not adhere. At this point, a black columu of smoke was seen ascending for several days in the spring of 1801, at a time when the summit was on all sides perfectly free from clouds. On the 16th March, 1802, Bonpland, Carlos Montufar, and myself reached a ridge of rock, covered with pumice-stone, and black, basaltic scoriæ in the region of perpetual snow, at an elevation of 2837 toises (18,142 feet), and consequently 2358 feet higher than Montblanc.

The snow was firm enough to bear us on

Bd. i, s. 200). With regard to the first origin of the opinion of the upheaval of solid masses in the form of heaped-up blocks, see Acosta, in the Viajes a los Andes Ecuatoriales par M. Boussin gault, 1849, pp. 222-223. The movement of the heaped-up fragments, induced by earth-shocks and other causes, and the gradual filling up of the interstices, may, according to the assumptions of the celebrated traveller, produce a gradual sinking of volcanic mountain peaks.

27 Humboldt, Asie Centrale, t. ii, pp. 296-301 (Gustav Rose, mineralgeognostische Reise nach dem Ural, dem Altai und dem Kasp. Meere, Bd. i, s. 599). Narrow, much elongated granitic walls may have risen, during the earliest foldings of the earth's crust, over fissures analogous to the remarkable, still open ones, which are found at the foot of the volcano of Pichincha: as the Guaycos of the city of Quito, of 30— 40 feet in width (see my Kleinere Schriften, Bd. i, s. 24).

28 La Condamine, Mesure des trois premiers Degrés du Meridien dans l'Hémisphère Austral, 1751, p. 56.

many points near the ridge of rock, which is so rare under the tropics (temperature of the atmosphere, 28°.8-34°.5). On the southern declivity, which we did not ascend, at the Piedro de Azufre, where scales of rock sometimes separate of themselves by weathering, masses of pure sulphur of 10-12 feet in length, and 2 feet in thickness, are found; sulphurous springs are wanting in the vicinity.

Although in the eastern Cordillera the volcano of Antisana, and especially its western declivity (from Ansango and Pinantura, towards the village of Pedregal) is separated from Cotopaxi by the extinct volcano of Passuchoa" with its widely distinguishable crater (la Peila), by the Nevado Sinchulahua and by the lower Rumiñaui, there is still a certain resemblance between the rocks of the two giants. From Quinche onwards the whole eastern chain of the Andes has produced obsidian, and yet el Quinche, Antisana, and Passuchoa belong to the basin in which the city of Quito is situated; whilst Cotopaxi bounds another basin, that of Lactacunga, Hambato and Riobamba. The small knot of mountains of the Altos of Chisinche separates the two basins like a dam; and what is remarkable

29 Passuchoa, separated by the farm el Tambillo from the Atacazo, does not any more than the latter attain the region of perpetual snow. The elevated margin of the crater, la Peila, has fallen in towards the west, but projects towards the east like an amphitheatre. The tradition runs that at the end of the sixteenth century, the Passuchoa, which had previously been active, ceased its manifestations of activity on the occasion of an eruption of Pichincha, which proves the communication between the vents of the opposite eastern and western Cordilleras. The true basin of Quito, closed like a dam,—on the north by a mountain group between Cotocachi and Imbaburo, and on the south, by the Altos de Chisinche (between 0° 20′ N. and 0° 41′ S.), is for the most part divided longitudinally by the mountain ridges of Ichimbio and Poingasi. To the eastward lies the valley of Puembo and Chillo; to the westward the plain of Inaquito and Turubamba. In the eastern Cordillera follow from north to south,-Imbaburo, the Faldas de Guamani, and Antisana, Sinchulahua, and the perpendicular, black wall, crowned with turret-like points, of Rumiñaui (Stone-eye); in the western Cordillera, Cotocachi, Casitagua, Pichincha, Atacazo, and Corazon, upon the slopes of which blooms the splendid Alpine plant, the red Ranunculus Gusmani. This has appeared to me to be the place to give, in brief terms, a morphological representation, drawn from iny own experience, of the form of a spot which is so important and classical in respect to volcanic geology,

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enough, considering its smallness, the waters of the northern slope of Chisinche pass by the Rios de San Pedro, de Pito, and de Guallabamba into the Pacific, whilst those of the southern declivity flow through the Rio Alaques and the Rio de San Felipe into the Amazons and Atlantic Ocean. The union of the Cordilleras by mountain knots and dykes (sometimes low, like the Altos just mentioned sometimes equal to Mont Blanc in height, as on the road over the Paso del Assuay) appears to be a more recent and also a less important phenomenon than the upheaval of the divided parallel mountain chain itself. As Cotopaxi, the greatest of the volcanoes of Quito, presents much analogy in its trachytic rock with the Antisana, so also we again meet with the rows of blocks (lines of fragments) which have already occupied us so long, even in greater number upon the slopes of Cotopaxi.

It was especially our business when travelling to trace these rows to their origin, or rather to the point where they are concealed beneath the perpetual covering of snow. We ascended upon the south-western declivity of the volcano from Mulalo (Mulahalo), along the Rio Alaques, which is formed of the Rio de los Baños and the Rio Barrancas, up to Pansache (12,066 feet), where we inhabited the spacious Casa del Paramo in the grassy plain (el Pajonal). Although up to this time much snow had fallen at night, we nevertheless got to the eastward of the celebrated Cabeza del Inga, first into the Quebrada and Reventazon de las Minas, and afterwards still further to the east over the Alto de Suniguaicu to the chasm of the Lion Mountain (PumaUrcu), where the barometer only showed an elevation of 2263 toises, or 14,471 feet. Another line of fragments which, however, we only saw from a distance, has moved from the eastern part of the snow-clad ash-cone towards the Rio Negro (an affluent of the Amazon) and Valle vicioso. It is uncertain whether these blocks were all thrown out of the crater at the summit to a great height in the air, as glowing, scoriaceous masses fused only at the edges (some angular, some rounded, of 6 or 8 feet in diameter, rarely conchoidal like those of Antisana), falling on the declivity of Cotopaxi and, hastened in their movement by the rush of the melted snow water; or whether, without passing through the air