198 THE ANDES OF SOUTHERN PERU 



of the volcanic field in a steep amphitheatre of majestic propor- 

 tions. 



Finally, we have the plateaus of the coastal zone. These are 

 plains with surfaces several thousand feet in elevation separated 

 by gorges several thousand feet deep. The Pampa de Sihuas is an 

 illustration. The post-maturely dissected Coast Eange separates 

 it from the sea. The pampas are in general an aggradational 

 product formed in a past age before uplift initiated the present 

 canyon cycle of erosion. Other plateaus of the coastal zone are 

 erosion surfaces. The Tablazo de lea appears to be of this type. 

 That at Arica, Chile, near the southern boundary of Peru, is 

 demonstrably of this type with a border on which marine plana- 

 tion has in places given rise to a broad terrace effect. 3 



3 The Physiography of the Central Andes, by Isaiah Bowman; Am. Journ. Sci., Vol. 

 28, 1909, pp. 197-217 and 373-402. See especially, ibid., Fig. 11, p. 216. 



