228 ANNALS NEW YORK ACADEMY OE SCIENCES 



COASTAL PLAIXS 



The distribution of the coastal plains may best be seen in the accom- 

 panying sketch map. They occupy three sections, which may be designated 

 as the northern, central and southern divisions. 



The northern division begins in the region of Tumbes, near the bound- 

 ary of Peru and Ecuador. It extends aloug the coast to the south, reach- 

 ing its maximum width in the cross section between Cerro del Yllesca 

 and Salitral. From this point to the south, it grows narrow quite rapidly 

 and finally ends at Salaverry. 



Going still farther south, we find but few remnants of what must have 

 been the inner edge of the coastal plain tucked away in partly drowned 

 valleys within the limits of the western slope. Between these valleys, 

 the formations composing the foothills of the western range now occupy 

 the present shore line and continue to do so, until we reach the region of 

 Canete. Here the coastal plain again makes its appearance. It can be 

 traced to a point just to the south of the mouth of the Eiver Yauca. 

 Here again the foothills of the western slope reach the present shore line. 



If we were to travel along the shore line from Yauca to the south, we 

 should be very much inclined to believe that, as far south as Ocona, the 

 actual foot-hills of the Cordillera again formed the present shore line. 

 This, however, we find not to be true. Should we pass up the Valley of 

 the Atico, we should find a belt of country some fifteen to twenty miles 

 wide occupied by Tertiary and post-Tertiary deposits, similar to those we 

 have seen to the north but standing at a higher altitude. They are deepl v 

 cut by the streams coming from the west range of the Andes. It is not 

 improbable that this belt may extend to and beyond the Valley of the 

 Chaparra. Going to the south, we can trace the elevated coastal plain, 

 where it is known under the various names of Paco Alto, Cuno-cuno, 

 south of the Valley of Ocofia, Pampa de la Joya, south of the Valley of 

 the Vitor, Pampa de Clemesi, south of the Tambo Valley, etc., and thus 

 continues with decreasing altitude to the southern boundary of Peru and 

 Chile. 



One of the additional features of the coastal plain is the frequent 

 occurrence of isolated hills and ridges near the present shore line. These 

 are locally known as "morros." They usually stand at an appreciable 

 elevation above the general level of the plain and hence form convenient 

 landmarks for determining direction of travel to a given point. 



With the exception of the section of the coastal plain to the north of 

 the Valley of the Ocona, the principle transverse streams have succeeded 

 in cutting only deep narrow valleys, with very little available floor for 



