MARSTERS, PHYSIOGRAPHY OF THE PERUVIAN ANDES 233 



deposits again form the shore line and continue with but little inter- 

 ruption to the southern terminus of the central division. From the 

 Pampas de Yunga, with an elevation of some 700 to 900 feet above sea 

 level, the surface gradually descends, until, at Lomas, it passes beneath 

 sea level. To the interior from Lomas, where the plain is known as Bella 

 Union, the surface is some 300 or more feet above sea level. In the valley 

 of the Eio Grande, sections of what appear to be late Tertiary may be 

 seen. On the coast near Santa Ana, similar sections may be found. On 

 the southwest flanks of Cerro Yunga, the same sediments are exposed. 

 In the interior, on the inner edge of the Pampa de Yunga, is the so-called 

 Valle de Carbonaria, where a considerable thickness of clays and sands, 

 presumably late Tertiary in age, may be seen. 



To the south of the plains bordering the Valley of Yauca, the foot- 

 hills once more form the present shore line. Nevertheless, in the mouth 

 of the Valley of Atiquipa and again in the Chala may be found a tri- 

 angular patch of what appear to be late Tertiary clays and sands: but 

 beyond this point the foothills seem to present a solid front, until we 

 reach the mouth of the Ocona Valley. This, however does not prove to 

 be the case. Should we enter the mouth of the Atico Valley and journey 

 in the direction of Caraveli, we should find that the supposed foothills of 

 west range of the Andes prove to be outliers, separated from the main 

 range by much-dissected plains made up of Tertiary and post-Tertiary 

 formations, and that these extend to the actual foothills of the Andes 

 in the vicinity of Caraveli. These plains probably pass to the northwest 

 as far as the valley of the Chaparra and represent the northwestern limit 

 of the south division of the coastal plains. The inner edge of this plain 

 is not less than 3,000 feet above sea level and has a width of twenty-five 

 miles or more. The pre-Tertiary coastal ridge as far as Ocoha shows' only 

 its highest point at elevations exceeding the general level of the interior 

 plain, while its shoreward flank has been nearly stripped of its post-Cre- 

 taceous covering. It is in sections on the Caraveli and tributaries to the 

 Atico that we find for the first time that mud flows of no mean propor- 

 tions enter into the formation of the coastal plain. In Quebrada Chin- 

 chin, we may see at least 300 feet of this flow exposed. Moreover, these 

 flows extended far in the direction of the coastal ridge. Prom the region 

 of the Atico section, we may trace the high plains to the southeast, being 

 represented by the Pampas de Paca Alta, Bourbon, etc., to the valley of 

 the Ocona; then we find the continuation in Pampas de Cuno-euno, 

 Majas and Vitor, where we reach the valleys of Siguas and Vitor. The 

 inner edges of these pampas stand at least 5,000 feet above sea level. 

 They are very deeply cut by the main streams coming from the West 



