Quito is celebrated as having been the scene of the measurement of a degree of the meridian by the French and Spanish mathematicians, in the reign of Louis the XV. The plain made choice of for the mensuration of the great base is situated 1592 feet lower than the city of Quito, and four leagues north-east of it, near the village of Yuranqui, from which it has its name. It was in this desert valley, surrounded by the lofty summits of the central Andes, that these geodesic operations were carried on, and which were attended with constant peril and labour; some idea of which may be formed from the following description of the chain of the Andes which pervades Quito; this chain after having been divided near Popayan into three branches, unites in the district of Pastos, and stretches far beyond the equator. Its most lofty summits form two lines, separated by a series of valleys, from 10,600 to 13,900 feet in height, as far as the third degree of south latitude, in which the chief towns of Quito are situated. On the west side of this vale or plain rise the mountains of Casitagua, Pichincha, Atacazo, Corazon, Ilinissa, Carguirazo, Chimborazo and Cunambay; and on the east are the peaks of Cayambe, Guamani, Antisana, Passuchoa, Ruminavi, Cotopaxi, Quelendama, Tunguragua and Capa Urcu, or the altar, all of which, excepting three or four, are higher than Mont Blanc, but on account of the great elevation of the plain on which they rest, their appearance is not so lofty as may be imagined; the summit of Chimborazo, the most elevated, not being more than 11,942 feet above the plain of Tapia, which itself is 9481 feet above the level of the sea. The constant temperature of the air is such, that the summits of those mountains which enter the region of perpetual snow have the line of congelation distinctly marked, and the road to Quito from Guayaquil leads along the northern declivity of Chimborazo, amid scenes of the most majestic nature, and near the regions of eternal frost. _Chimborazo_, the most lofty of the American summits is in the form of a dome, and towers over the conical peaks and heads of the adjacent mountains, to an amazing altitude; its height above the level of the sea being 21,441 feet.