146 THE ANDES OF SOUTHERN PERU 



walls of the gorge preventing the escape of the cattle. To these 

 are driven the market cattle, or mules and burros that are re- 

 quired for relays along the shore trail. 



Stream 2 heads in the belt of rains. Furthermore it is a much 

 older stream than 1, since it dates back to the time when the Coast 

 Kange was first formed. It has ample tributary slopes and a large 

 number of small valleys. A trickle of water flows down to become 

 lost in the alluvium of the lower part of the valley or to reappear 

 in scattered springs. Where springs and seepage occur together, 

 an olive grove or a garden marks the spot, a corral or two and a 

 mud or stone or reed hut is near by, and there is a tiny oasis. 

 Some of these dots of verdure become so dry during a prolonged 

 drought that the people, long-established, move away. To others 

 the people return periodically. Still others support permanent 

 settlements. 



Stream 3 has still greater age. Its only competitors are the 

 feeble, almost negligible, streams that at long intervals flow east 

 toward the dry zone. Hence it has cut back until it now heads in 

 the desert. Its widely branched tributaries gather moisture from 

 large tracts. There is running water in the valley floor even down 

 in the terrace zone. At least there are many dependable springs 

 and the permanent homes that they always encourage. A valley 

 of this type is always marked by a well-defined trail that leads 

 from settlement to settlement and eastward over the "pass" to 

 the desert and the Andean towns. 



Stream 4 is a so-called "antecedent" stream. It existed be- 

 fore the Coast Eange was uplifted and cut its channel downward 

 as the mountains rose in its path. The stretch where it crosses 

 the mountains may be a canyon with a narrow, rocky, and unculti- 

 vable floor, so that the valley trails rise to a pass like that at the 

 head of stream 3, and descend again to the settlements at the 

 mouth of 4. There is in this last type an abundance of water, for 

 the sources of the stream are in the zone of permanent snows and 

 frequent winter rains of the lofty Cordillera of the Andes. The 

 settlements along this stream are continuous, except where shut- 

 ins occur — narrow, rocky defiles caused by more resistant rock 



