CuAP. XII. GEOGRAPHICAL FEATURES. 215 



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, tlu'ough Caravaya, to 

 Bolivia. These rocks throw off spurs along the eaiitern side 

 of the main chain. Of this formation, too, arc the loftiest 

 mountain-peaks in South America: — lUampu, or Sorata 

 (24,812 feet), and Illhnani (24,155 feet). lUampu, Mr. 

 Forbes assures us, is fossiliferous up to its very summit.* 



Such is a brief account of the geography of Caravaya, and 

 especially of the streams which combine to form the great 

 river Pm'us, 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 aimferous, they flow through 

 forests abomiding in valuable products, and through countries 

 of inexhaustible capabiHties. Yet the coui'ses of veiy 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 xVmazon, may be said to be eutu'ely 

 unknown to geographers. 



* On the Geology of Bolivia and Sorata contain fossils, and consist of 

 Southern Peru, by David Forbes, Esq., blue-cIay shales, micaceous slates, 

 in the Joiu-nal of the Geological Society gi-auwacke, and clay slates, with gold- 

 for Feb. 1861, p. 53. bearing quartz, metallic bismuths, iron- 

 Mr. Forbes had, of comse, person- ore, and argentiferous galena. " The 

 ally examined only a portion of this whole of this Silm-iaii formation is eiui- 

 great Silmian region. At Tipuani, in nently aiuifcrous, and contains every- 

 Bolivia, there is a very rich auriferous where frequent veins of auriferous 

 country, composed of blue-clay slates, quartz, usiwlly associated with iron 

 with no fossils; wlule the beds near pyrites." 



