238 ANNALS NEW YORK ACADEMY OF SCIENCES 



pendent upon the amount of available water. In the Pacasmayo case we 

 find an additional feature worthy of mention. At the contact of the 

 coastal plain with the foothills, the valley has not been deeply incised. 

 On both sides of the valley are extensive plains, composed largely of the 

 waste from the edge of the foothills, plus the original surface of the 

 coastal plain. So near are these plains to the level of the river, but a 

 short distance within the foothills, that water has been diverted from its 

 legitimate place on the valle} r -floor to irrigate large stretches of plain on 

 either side of the valle}^. Success in this attempt has been foiled, in part, 

 by the lack of water for the extent of territory taken up on the one hand 

 and the strong tendency to salinity of large tracts of the plains on the 

 other. 



It is onty where the coastal plain has undergone the minimum amount 

 of elevation that we find the last distinct stage to be described. This is 

 fairly well illustrated by the Eten-Lambayeque-Motupe plains, where we 

 have a group of small streams coming from the interior to a slightly ele- 

 vated plain. Only along the inner contact of the coastal plain with the 

 foothills have these streams slightly incised themselves, but as they ex- 

 tended outward and over the plain they actually spread their waste over 

 large areas. Under such physiographical relations, we have the condi- 

 tions for the development of the most important rice industry in the 

 entire Eepublic of Peru. The rice fields occupy the fluviatilly aggraded 

 portions and such adjacent parts of the original plain as may be reached 

 by the amount of water available. The growth of sugar cane has also 

 become an important industry. Where the main streams have formed a 

 well-defined valley-floor, the predominant culture is of maize, alfalfa and 

 the staple vegetable products for the markets of the principal towns. 



In the valley of the Piura, we find a slightly incised valley, the floor of 

 which is occupied by cotton culture, as the foremost industry, throughout 

 its upper stretches. Notable lack of water has limited the territory under 

 cultivation. Piura and Catacaos are located at these points. Again we 

 find this portion of the valley-floor near the inner edge of the coastal 

 plain. The lower portion of the Piura Valley has spread itself over the 

 plain. Not enough water reaches this part to assure crops. The town 

 of Sechura is located near the mouth of this sand-laden water-way. The 

 people here can maintain themselves only in part by agricultural work. 

 Not a small part of the inhabitants is engaged in transportation, fishing 

 and salt-mining. 



