putation of furnishing no lava-streams, but only incoherent, glowing scoriaceous masses, thrown out of the single summital crater, and often rolling down in a linear arrangement. This was even the opinion22 of La Condamine, when he left the highlands of Quito and Cuença in the spring of 1743. Fourteen years afterwards, when he returned from an ascent of Vesuvius (4th June, 1755), in which he accompanied the sister of Frederick the Great, the Margravine of Baireuth, he had the opportunity of expressing himself warmly, in a meeting of the French Academy, upon the want of true lava-streams (laves coulées par torrens de matières liquefiées)

22 "I have never known," says La Condamine, "lava-like matter in America, although M. Bouguer and myself have encamped for whole weeks and months upon the volcanoes, and especially upon those of Pichincha, Cotopaxi, and Chimborazo. Upon these mountains I have only seen traces of calcination, without liquefaction. Nevertheless, the kind of blackish crystal, commonly called Piedra de Gallinaço in Peru (obsidian), of which I have brought home several fragments, and of which a polished lens of seven or eight inches in diameter, may be seen in the cabinet of the Jardin du Roi, is nothing but a glass formed by volcanic action. The materials of the stream of fire which flows continually from that of Sangai, in the province of Macas, to the southeast of Quito, are no doubt lava, but we have only seen this mountain from a distance, and I was no longer at Quito at the time of the last eruptions of the volcano of Cotopaxi, when vents opened upon its flanks, from which ignited and liquid matters were seen to issue in streams, which must have been of a similar nature to the lava of Vesuvius" (La Condamine, Journal de Voyage en Italie, in the Mémoires de l'Acad. des Sciences, 1757, p. 357, Historie, p. 12). The two examples, especially the first, are not happily chosen. The Sangay was first scientifically examined in December of the year 1849, by Sebastian Wisse; what La Condamine, at a distance of 108 miles, took for luminous lava flowing down, and "an effusion of burning sulphur and bitumen," consists of red-hot stones and scoriaceous masses, which sometimes, pressed closely together, slip down on the steep declivities of the cone of ashes (Cosmos, see above, p. 264). On Cotopaxi, as on Tungurahua, Chimborazo, and Pichincha, or on Puracé, and Sotara near Popayan, I have seen nothing that could be looked upon as narrow lava-streams, which had flowed from these colossal mountains. The incoherent, glowing masses of 5-6 feet in diameter, often containing obsidian, which Cotopaxi has scattered abroad during its eruptions, impelled by floods of melting snow and ice, have reached far into the plain, where they form rows partially diverging in a radiate form. La Condamine also says very truly elsewhere (Journal du Voyage à l'Equateur, p. 160):-"These fragments of rock, as large as the hut of an Indian, form series of rays, which start from the volcano as from a common centre."

from the volcanoes of Quito. The Journal d'un Voyage en Italie, which was read at the meeting of the 20th April, 1757, only appeared in 1762 in the Mémoires of the Academy of Paris, and is of some geognostic importance in the history of the recognition of old extinct volcanoes in France, because in this journal, La Condamine, with his peculiar acuteness, and without knowing of the certainly earlier observations of Guettard,23 expresses himself very decidedly upon the existence of ancient crater-lakes and extinct volcanoes in middle and northern Italy and in the south of France.

This remarkable contrast between the narrow and undoubted lava-streams of Auvergne thus early recognized, and the often too absolutely asserted absence of any effusion of lava in the Cordilleras, occupied me seriously during the whole period of my expedition. All my journals are full of considerations upon this problem, the solution of which I long sought in the absolute elevation of the summits and in the vastness of the circumvallation, that is to say, the sinking of trachytic conical mountains from mountain-plains of eight or nine thousand (8500-9600 English) feet in elevation and of great breadth. We now know, however, that a volcano of Quito, 17,000 feet in height, which throws out scoriæ (that of Macas), is uninterruptedly much more active than the low volcanoes Izalco and Stromboli; we know that the eastern dome-shaped and conical mountains, Antisana and Sangay, have free slopes towards the plains of the Napo and Pastaza; and the western ones, Pichincha, Iliniza, and Chimborazo, towards the affluents of the Pacific Ocean. In many also the upper part projects without circumvallation eight or nine thousand feet above the elevated plateaux. Moreover, all these elevations above the sea-level, which is regarded, although not quite correctly, as the mean elevation of the earth's surface, are certainly inconsiderable as compared with the depth which we may assume to be that of the seat of volcanic activity, and of the necessary temperature for the fusion of rock-masses.

23 Guettard's memoir on the extinct volcanoes was read at the Academy in 1752, consequently three years before La Condamine's journey into Italy; but only printed in 1756, consequently during the Italian travels of the astronomer.

The only phenomena resembling narrow lava-eruptions which I discovered in the Cordilleras of Quito, are those presented by the colossal mountain Antisana, the height of which I determined to be 19,137 feet (5833 metres), by a trigonometrical measurement. As the structure furnishes the most important criterion here, I will avoid the systematic denomination lava, which confines the idea of the mode of production within too narrow limits, and make use, but quite provisionally, of the names "rock-débris" (Felstrümmern) or "detritus dykes," (Schuttwällen, traînées de masses volcaniques). The mighty mountain of Antisana, at an elevation of 13,458 feet, forms a nearly oval plain, more than 12,500 toises (79,950 feet) in long diameter, from which the portion of the mountain covered with perpetual snow rises like an island. The highest summit is rounded off and dome-shaped. The dome is united by a short jagged ridge with a truncated cone lying towards the north. In the plateau, partly desert and sandy, partly covered with grass (the dwelling-place of a very spirited race of cattle, which, owing to the slight atmospheric pressure, easily expel blood from the mouth and nostrils when excited to any great muscular exertion), is situated a small farm (Hacienda), a single house in which we passed four days in a temperature varying between 38° 6 and 48.2. The great plain, which is by no means circumvallated as in craters of elevation, bears the traces of an ancient sea-bottom. The Laguna Mica, to the westward of the Altos de la Moya, is to be regarded as the residue of the old covering of water. At the margin of the limit of perpetual snow, the Rio Tinajillas bursts forth, subsequently, under the name of Rio de Quixos, becoming a tributary of the Maspa, the Napo, and the Amazon. Two narrow, wall-like dykes, or elevations, which I have indicated upon the plan of Antisana, drawn by me, as coulées de laves, and which are called by the natives Volcan de la Hacienda and Yana Volcan (Yana signifies black or brown in the Qquechhua language), pass like bands from the foot of the volcano at the lower margin of the perpetual snow-line, and extend, apparently with a very moderate declivity, in a direction N.E.-S.W., for more than 2000 toises (12,792 feet) into the plain. With very little breadth they have probably an elevation of 192 to 213 feet above the soil of the Llanos de la Ha

cienda, de Santa Lucia, and del Cuvillan. Their declivities are everywhere very rugged and steep, even at the extremities. In their present state they consist of conchoidal and usually sharp-edged fragments of a black basaltic rock, without olivine or hornblende, but containing a few small white crystals of felspar. The fundamental mass has frequently a lustre like that of pitchstone, and contains an admixture of obsidian, which was especially recognizable in very large quantity, and more distinctly, in the so-called Cueva de Antisana, the elevation of which we found to be 15,942 feet. This is not a true cavern, but a shed formed by blocks of rock which had fallen against and mutually supported each other, and which preserved the mountain cowherds and also ourselves during a fearful hailstorm. The Cueva lies somewhat to the north of the Volcan de la Hacienda. In the two narrow dykes, which have the appearance of cooled lavastreams, the tables and blocks appear in part inflated like cinders or even spongy at the edges, and in part weathered and mixed with earthy detritus.

Analogous but more complicated phenomena are presented by another also band-like mass of rocks. On the eastern declivity of the Antisana, probably about 1280 feet perpendicularly below the plain of the Hacienda in the direction of Pinantura and Pintac, there lie two small round lakes, of which the more northern is called Ansango, and the southern Lecheyacu. The former has an insular rock, and is surrounded by rolled pumice-stone, a very important point. Each of these lakes marks the commencement of a valley; the two valleys unite, and their enlarged continuation bears the name of Volcan de Ansango, because from the margins of the two lakes narrow lines of rock débris, exactly like the two dykes of the plateau which we have described above, do not, indeed, fill up the valley, but rise in its midst like dams to a height of 213 and 266 feet. A glance at the local plan which I published in the "Geographical and Physical Atlas" of my American travels (pl. 26), will illustrate these conditions The blocks are again partly sharp-edged, and partly scorified and even burnt like coke at the edges. It is a basaltic, black, fundamental mass, with sparingly scattered glassy felspar; some fragments are blackish brown and of a dull pitch stone-like lustre. Basaltic as the fundamental mass

appears, however, it is entirely destitute of the olivine which occurs so abundantly on the Rio Pisque and near Guallabamba, where I saw basaltic columns of 72 feet in height and 3 feet thick, which contained both olivine and hornblende scattered in them. In the dyke of Ansango numerous tablets, cleft by weathering, indicate porphyritic slates. All the blocks have a yellowish gray crust from weathering. As the detritus-ridge (called los derrumbamientos, la reventazon, by the natives, who speak Spanish), may be traced from the Rio del Molina, not far from the farm of Pintac, up to the small crater-lakes surrounded by pumice-stone (chasms filled with water), the opinion has grown up naturally, and, as it were, of itself, that the lakes are the openings from which the blocks of stone came to the surface. A few years before my visiting the district, the ridge of fragments was in motion for weeks upon the inclined surface, without any perceptible previous earthquake, and some houses near Pintac were destroyed by the pressure and shock of the blocks of stone. The detritus-ridge of Ansango is still without any trace of vegetation, which is found, although very sparingly, upon the two more weathered and certainly older eruptions of the plateau of Antisana.

How is this mode of manifestation of volcanic activity, the action of which I am describing, to be denominated ?24 Have we here to do with lava-streams? or only with semiscorified and ignited masses, which are thrown out unconnected, but in chains pressed closely upon each other (as on Cotapaxi in very recent times)? Have the dykes of Yana Volcan and Ansango been perhaps merely solid fragmentary masses, which burst forth without any fresh elevation of temperature from the interior of a volcanic conical mountain, in which they lay loosely accumulated and therefore badly supported, their movement being caused by the concussion of an earthquake, impelled by shocks or falls and giving rise to small local earthquakes? Is no one of the three manifes

24There are few volcanoes in the chain of the Andes," says Leopold von Buch, "which have presented streams of lava, and none have ever been seen around the volcanoes of Quito. Antisana, upon the eastern chain of the Andes, is the only volcano of Quito upon which M. de Humboldt saw, near the summit, something analogous to a stream of lava; this stream was exactly like obsidian" (Descr. des Iles Canaries, 1836, pp. 468 and 488).