GEOLOGY OF PERU—ADAMS. 419 
creased volume of the streams and the erosion which accom- 
panied the glacial period.¢ 
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. 
