Between the Pass of Chacabuco north of Santiago, the capital of Chile, and the archipelago of Chiloe, a chain of hills, composed in general of crystalline rocks, borders the coast; between which and the Andes exists a longitudinal valley, well watered by the rivers descending from the central chain, and which constitutes the most fertile portion, nay the garden of the Chillian republic—the rich provinces of Santiago, Colchagua, and Maule. This longitudinal depression may be considered as a prolongation of the strait that separates Chiloe from the mainland. Many peaks of the Andes enter within the limits of perpetual snow, between the 40th and 31st parallels; and some of which are active volcanos. In lat. 32° 39ʹ rises the giant of the American Andes, the Nevado of Aconcagua, which towers over the Chillian village of the same name, and is so clearly visible from Valparaiso. Although designated as a volcano, a term generally applied in Chile to every elevated and snowy peak, it offers no trace of modern igneous origin. It appears to be composed of a species of porphyry generally found in the centre of the Chillian chain. Its height, according to Captain Beechey’s very accurate observations, exceeds 24,000 feet.[41] About the latitude of Concepcion the dense forests of Araucarias and of other semi-tropical plants cease with the humid equable climate; and as no rain falls in central Chile for nine months in the year, the brown, purple, and tile-red hills and mountains are only dotted here and there with low trees and bushes; very soon, however, after the heavy showers have moistened the cracked ground, it is covered with a beautiful but transient flora. In some valleys it is more permanent and of a tropical character, mixed with alpine plants.[42] In southern Chile rain falls only once in two or three years, the consequence of which is sterility on the western precipitous and unbroken descent of the Andes; but on the east, two secondary branches leave the central Cordillera, which extend 300 or 400 miles into the plains, wooded to a great height. The Sierra de Cordova, the most southern of these, begins between the 33d and 31st parallels, and extends in the direction of the Pampas; more to the north, the Sierra di Salta and Juguy stretches from the valley of Catamarca and Tucuman towards the Rio Vermejo, one of the tributaries of the Rio de la Plata. The chain takes the name of the Peruvian Andes about the 24th degree of south latitude, and is separated from the Pacific by a range of hills composed of crystalline rocks, and parallel to the sea coast, and of an intervening sandy desert, seldom above 60 miles broad, on which rain scarcely ever falls, where bare rocks pierce through the moving sand. The width of the coast is nearly the same to the Isthmus of Panamá, but damp luxuriant forests full of orchideæ, begin about the latitude of Payta, and continue northwards.