236 ANNALS NEW YORK ACADEMY OF SCIENCES 



Locus of Agriculture and its Dependency upon Physiographic Phe- 

 nomena. — In these days, much is said about physiographic features as 

 determinative factors in the location of human industries. A word con- 

 cerning the distribution of agriculture on the coastal plain is worth 

 while. 



Mention has already been made of the differential elevation which the 

 coastal plains of Peru have suffered. Where the elevation has reached its 

 maximum, or where the plain has been aggraded to a much greater ele- 

 vation, as by the addition of lava flows, the present streams coming from 

 the flanks of the oldland (the west slope of the Andes) have cut out verit- 

 able canyons.. Time enough has not yet elapsed to permit these streams to 

 widen their floors to any appreciable extent. Here and there in some of 

 the canyons, the stream has reached the underlying oldland and its rate 

 of erosion has been retarded. Above this point, the stream has thus had 

 some opportunity to do some side cutting and hence has widened its floor ; 

 only at these points do we see man availing himself of the agricultural 

 opportunities offered him. In proportion as the elevation has been less 

 so in a general way, we may say that transverse master streams have had 

 a chance to make floor room for the use of man. Let us take a few ex- 

 amples to illustrate the principal stages and their physiographic bearing 

 on the topic in hand. Probably the maximum elevation of the coastal 

 plains of Peru was attained in the Mollendo-Arequipa, or Vitor, section. 

 While formations entering into the structure of this section are in pari; 

 sedimentary in origin, it is not assumed that the present elevation of its 

 surface above sea level represents the actual uplift above that plane. It 

 is very probable that this part of the plain has actually been aggraded 

 by a lava flow, or flows, the present surface of which never stood at sea 

 level, although the loAver part of the earlier flows may have reached the 

 edge of the Tertiary sea. At all events, the Chile- Yitor stream coming 

 from the high plateaus to the interior have, within the limits of the 

 coastal plain, succeeded in cutting a very deep canyon. Further, it has 

 developed its widest floor near the contact of the inner edge of the 

 plain with the pre-Tertiary oldland, or the foothills of the West Eange 

 of the Andes. F<jr that reason we have Quercotilla, an agricultural com- 

 munity and a village, located at this point. Within the remainder of this 

 valley to the sea, we do not find a single town until we reach the present 

 shore line, where Quilca, a small village, is not placed on the valley floor, 

 but to one side in a deep-water embayment of fiord-like character. This 

 little village is here for the dispatch by water of agricultural products 

 from the valleys of Camana and Ocona, neither of which possesses a safe 

 port of entrance. Mention has also been made of the special case of 



