part 3] THROUGH THE ANDES OE PERU AND BOLITIA. 247 



along the route to Chanclioma3^o. After the longitudinal valley 

 of the Mantaro has been crossed, a second and subsidiaiy watershed 

 is met with at 14,000 feet, from which a steep descent is made 

 down the Tarma valley. About 25 miles beyond the village of 

 that name, at the Tambo of Huacapistana, are encountered the 

 first signs of luxuriant vegetation, denoting the western limit of 

 the Montaiia district. The scenery at this point is very similar 

 to that of a typical valle}^ in the Swiss Alps ; but with a further 

 descent the temperature rapidly increases, and the tropical cha- 

 racter of the flora becomes pronounced. 



At San Kamon the Tarma River is joined by the Tulomayo to 

 form the Chanchomayo, and this in turn unites with the Paucar- 

 tambo to form the River Perene, one of the headwaters of the 

 Amazonian system. This point, which forms the eastern limit 

 of the section, although distant more than 2000 miles from the 

 Atlantic coast, is onh'' 1145 feet above sea-level. 



The earliest-recorded observations on the geology of the Lima 

 district were those made by Charles Darwin during the voyage of 

 the ' Beagle ' in 1835, which dealt chiefly with the evidence as to 

 recent uplift afforded by the kitchen-middens of the island of San 

 Lorenzo. Little attention, however, seems to have been paid to 

 the structure of the mountainous region of the mainland until the 

 beginning of the present centur}^, when the first definite account of 

 its geological features, illustrated by a section across the Cordillera, 

 was published b}^ Prof. Gustav Steinmann as the result of a journey 

 made in 1904 from Lima to the Chanchomayo River.i Of late 

 years our knowledge of the district has been further enriched by 

 the writings of Prof. Carlos 1. Lisson, of Lima, who has made a 

 detailed study of the country in the immediate neighbourhood 

 of the capital. 



In view of the fact that m.y route across this part of the Andes 

 was identical with that taken by Steinmann, although continued 

 some miles farther towards the east, anything more than a sum- 

 marized account of my observations does not appear to be necessary, 

 except in so far as they afford additional evidence for the facts 

 already recorded. In many cases, however, the views of that 

 author are not in accordance with mine, and I have therefore been 

 led to give an independent interpretation of the section, in order 

 lo illustrate the points upon which we appear to differ. It is only 

 fair to add that more than once I have been able to strengthen or 

 confirm my views on obscure facts by reference at a later date to 

 his paper mentioned above. 



A preliminary study of the phj^'sical features of this part of the 

 country shows that they differ markedly in character from those 

 prevailing in the South of Peru and the North of Chile, as described 

 by me in former papers of this series. Pour principal topographic 



1 See Bibliography, p. 282, § IV, No. 46. 



