The most remarkable circumstance in the geological features of the South American continent is the vast development of volcanic force, which is confined to the chain of the Andes, and where it has acquired a considerable breadth, as in the Peru-Bolivian portion, to the part nearest the sea-coast. It would be wrong, however, to say that there are no traces of modern volcanic action at a great distance from the sea:[54] it is one of those theories which recent discoveries in both continents have proved the fallacy of. The volcanic vents occur in the Andes in linear groups: the most southern of these is that of Chile, extending from the latitude of Chiloe to that of Santiago, 42° to 33° S.: in this space exist five well-authenticated craters in ignition—the most southern is the volcano of Llanquihae or Osorno, observed by M. Gaye, and the most northern that of Maypu, the fires of which are sometimes seen from the capital of Chile. Between the 32d parallel and the Bolivian frontier there does not appear to be a single volcanic vent, but in the province of Atacama rises the volcano of San Pedro of Atacama. The mountain of Isluga, in the province of Tarapaca, is said to be an active volcano, but the great centre of volcanic action in this part of the Western Cordillera extends from 18° 10ʹ to 16° 20ʹ, where the Andes have changed their direction from being parallel to the meridian to one inclined nearly 45 degrees to that line. The trachytic giant domes of the Andes, Sahama, and the Nevado of Chuquibamba mark the N. and S. limits of this line of vents: the former, one of the most perfect trachytic pyramids in the Andes, rises to a height of 22,350 feet, in lat. 18° 7ʹ and long. 68° 54ʹ W.; near to it are the twin Nevados of Pomarape and Parinacota, one of which appears to emit smoke. The group of snowy peaks seen from Arica, the centre of which, the Nevado of Tacora, is in lat. 17° 43ʹ, offers a broken-down crater, and an active solfaterra, on one of its sides. Between this point and the volcano of Arequipa no active volcano has been observed. It is well known that the latter has vomited flames and ashes, and spread desolation around, at a comparatively recent period; the crater of Uvinas, active in the 16th century, is now filled up and completely extinct. Between the latitude of Arequipa (16° 24ʹ) and the Equatorial group of volcanos, the Andes do not present a single active crater. This Equatorial group extends over a meridional line of 3-1/4 degrees—between the Peak of Sangay and the volcano of Los Pastos. The most remarkable of these volcanic vents are the Sangay, Tunguragua, and Cotopaxi, all situated in the Cordillera most remote from the ocean. Pichincha burned as recently as 1831; and north of the Equator, Imbaburu, the volcanos of Chiles, of Cumbal, of Tuqueres or Los Pastos, of Sotara and Purace, mark the extension of actual volcanic action into our hemisphere.