But some of these villages are at greater distances from the foot of the Andes than others; thus they are not in a straight line, and the direct distance from Ollachea to the Bolivian frontier is a good deal under 180 miles. The valleys in which the Caravaya villages are situated are separated from each other by spurs of the Andes, many of them so wild and precipitous as to be quite inaccessible; and there is no means of passing from village to village, in many instances, without crossing the Andes to Crucero or Macusani, and descending again by another pass. For this reason Crucero, being in the most central position, has been chosen as the site of the capital of the province, though in a bleak and intensely cold region. The geological formation of Caravaya is composed of non-fossiliferous schists, micaceous and slightly ferruginous, with veins of quartz. It is a portion of the extensive system of rocks which Mr. Forbes has grouped together as belonging to the Silurian epoch, and which extends almost continuously over an extent from north-west to south-east of more than seven hundred miles, forming the mountain-chain of the Eastern Andes, continuous from Cuzco, through Caravaya, to Bolivia. These rocks throw off spurs along the eastern side of the main chain. Of this formation, too, are the loftiest mountain-peaks in South America:--Illampu, or Sorata (24,812 feet), and Illimani (24,155 feet). Illampu, Mr. Forbes assures us, is fossiliferous up to its very summit.[307] Such is a brief account of the geography of Caravaya, and especially of the streams which combine to form the great river Purus, from the rivers of the Paucartambo valley on the extreme north-west, to the Pablo-bamba on the frontier of Bolivia. The streams flowing from the Eastern Andes to the north-west of the Paucartambo system combine to swell the Ucayali, while those to the south-east of the Pablo-bamba fall into the Beni, one of the chief tributaries of the Madeira. The intermediate streams are the sources of the unknown Purus, they are all more or less auriferous, they flow through forests abounding in valuable products, and through countries of inexhaustible capabilities. Yet the courses of very few of them have been explored to distances of seventy miles from their sources, and the main stream of the Purus, one of the principal affluents of the Amazon, may be said to be entirely unknown to geographers. CHAPTER XIII. CARAVAYA.--THE VALLEY OF SANDIA.