6 MB. J. A. DOUGLAS O^" GEOLOGICAL SECTIONS [vol. lxxvi r 



Fording the River Sumbay, we rejoined the line at Pueacaneha l 

 (kil. 180), and, continuing to ascend, reached its summit at Crucero 

 Alto (kil. 187, alt. 14,667 feet). 



The descent on the eastern side is at first gradual, then more 

 abrupt to Santa Lucia (kil. 238, alt. 13,250 feet), passing on 

 the way over the narrow neck of land between the twin lakes of 

 Lagunillas and Saracocha. 



From Santa Lucia to the copper-mines of Maravillas the river- 

 valley, along which the line is built, is comparatively broad, its 

 floor being covered by a thick deposit of alluvial gravel. Beyond 

 this point, however, it narrows considerably, and is flanked on both 

 sides by hills of steeply-dipjring stratified Palseozoic rocks, on the 

 upturned edges of which rests a younger Mesozoic series. This- 

 striking unconformity is a conspicuous feature of the landscape, 

 and can be clearly seen from the passing train. 



The country north of Puno furnishes little of geological or 

 topographical interest, comprising as it does the broad alluvial 

 swamps left by the receding waters of Lake Titicaca ; we, there- 

 fore, left the line after reaching Taya Taya in favour of the more 

 direct route south-eastwards by the hacienda of Yanarico and Vilque, 

 where the trail is flanked by isolated flat-topped hills which owe 

 their form to a capping of lava. 



The final descent into Puno (alt. 12,540 feet) affords a magnifi- 

 cent view of the lake, backed by the snow-clad peaks of the 

 Bolivian Cordillera in the far distance. 



For the continuation of our traverse we proceeded along the line 

 to Cuzco as far as the village of Tirapata, and thence journeyed 

 north-eastwards into the region drained by the head- waters of the 

 Amazon, along the trail of the Inambari gold and rubber companies. 



I have previously shown that the Eastern Cordillera of Bolivia 

 constitutes a well-defined range of high peaks, formed of granite 

 and Palaeozoic sediments — Mount Illimani, Huaina Potosi, etc. In 

 the district under discussion, however, such is no longer the case ; 

 individual peaks, recognizable on a map, are of rare occurrence and 

 scattered over a wide area, and the Cordillera here consists of a 

 number of intersecting ridges which unite farther north in the so- 

 called 'Vilcanota knot.' On the route mentioned above, the divide 

 is crossed at about 15,500 feet, between a little river known as 

 "Viscachani and the village of Macusani. 



Some 20 miles or more north-east of this point, two much higher 

 snow-capped peaks are visible, the altitudes of which have 

 apparently never been determined. The}" are known to the natives 

 as Mount Allincapacc and Mount Huainacapacc, and if we judge 

 from the amount of snow on their summits, they must at least 

 rival some of the better-known peaks of Bolivia. 



After leaving Macusani. a rapid descent is made down the valley 

 of the San Graban River, famous as the source of much Spanish 

 gold. This valley shows a very immature stage of development. 



1 Distances are henceforward reckoned from Arequipa. 



