GEOLOGY OF PEEU — ADAMS. 419 



creased volume of the streams and the erosion which accom- 

 j)anied the glacial jDeriod.* 



RECENT FORMATIONS OF THE COAST. 



The recent formations consist principally of materials transported 

 by the rivers and deposited at their deltas and of the wind-blown 

 sands which sweep over the coastal plains. In addition there are 

 places along the coast where the materials eroded by wave action 

 and transported by ocean currents have accumulated in the form of 

 recent beaches. The beaches here referred to should not be con- 

 founded with the raised beaches, which will be discussed later in this 

 paper. The deltas of the coast are usually unsymmetrical because 

 of the northward direction of the coast currents. In many cases 

 the deltas blend with the recent beaches, due to marine action. The 

 delta of the Tumbez River, which is the northernmost of the coast, 

 lies in front of a clearly defined sea cliff. Similarly the delta of the 

 Chira River blends with the recent sea beaches lying in front of a 

 sea cliff, which extends from the mouth of the river northward to 

 Negritos. 



The remaining rivers of the northern coastal plains do not have 

 deltas worthy of special mention. In the extent of mountainous 

 coast between the northern coastal plains and the south central 

 coastal plains there are a number of localities where recent beaches 

 may be found, and in this part of the coast the Quaternary and 

 Tertiary deposits already described are absent. 



To the north of the Santa River there is an area of recent beaches 

 in which salt is manufactured by evaporation, the brine being ob- 

 tained by digging shallow pits, into which it filters. The area of the 

 beaches is extensive, and the slight depth to the salt water indicates 

 the fact that they are but slightly above sea level. The materials 

 which have accumulated and formed the beaches have largely been 

 brought by the Santa River and drifted northward by the ocean 

 currents. The immediate delta of the Santa River has extended sea- 

 ward and so connected an island with the mainland. In Chimbote 

 and Samanco harbors one may see an area of drowned mountainous 

 coast. At some former time the two bays were one, but the accumu- 

 lation of sand has formed a bar and connected one of the larger 

 islands with the mainland. The front of the raised delta of the 

 Rimac River, on which Lima, the capital of the country, is located, 

 has been largely cut away by marine erosion, and the currents have 

 drifted the materials northward, forming the spit of land called la 

 Punta, which is a feature of the harbor of Callao. This spit is 



"A description of the Rimac delta by the author may be found in Bulletin 

 No. 33 of the Corps of Engineers of Mines of Peru, published in 1905. 



