420 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1908. 



gradually extending, and lying between it and the island of San 

 Lorenzo there is now a bank on which the waves break. The ultimate 

 outcome of this process may be a connection between the mainland 

 and San Lorenzo Island. 



At Port Cerro Azul the rocky promontory which protects the 

 port was once an island. It has been connected with the mainland 

 by the growth of the delta of the Canete River. Similarly there are 

 a number of delta deposits and recent beaches in the southern part of 

 the coast. In riding on a train from Mollendo along the beach before 

 the ascent of the range of coast hills is made one may see recent con- 

 glomerates, which have been partially eroded, and marine beaches 

 in process of formation. 



The material transported by the winds has in places accumulated 

 in areas of sand dunes which are moving wdth the general direction 

 of the wind, but the more common condition is to find the sand form- 

 ing a mantle on the hill slopes and rounding the contours of the hills, 

 and often rising well up on to the sides and in some cases even to the 

 crests of the mountains. The most extensive area of drifting sand is 

 to be found in the Sechura Desert and the plains to the east of Piura. 

 In the latter place the sand is held by a sparse growth of drouth- 

 resisting trees and bushes. The height of this drifting sand as seen 

 in the topography of the country reaches perhaps 200 feet, but proof 

 of its gi-eat thickness was obtained when a well was drilled in it. 

 The drillers could hardly be expected to distinguish the point at 

 which they passed out of the wind-drifted sand, but they found 

 nothing but sand and had no difficulty in driving the casing of the 

 well to a depth of something over 3,000 feet. 



If one refers to the map of the coast of Peru and observes the con- 

 figuration of the coast in the region of the desert of Sechura, he will 

 see that the direction changes more to the west so that the winds blow- 

 ing from the Pacific have a clean sweep over the desert, and the sand 

 is carried inland by the winds in a nearly northern direction. It is 

 this fact which accounts for the low relief near the coast where the 

 sand has been derived and the great thickness of the Aeolian deposits 

 to the east of Piura. 



In the south central coastal plains there is a conspicuous area of 

 sand hills between lea and Pisco; also some smaller ones to the west 

 of lea and Palpa. There are numerous areas of migrating sand hills 

 in the southern coastal plains, but none of the dunes attain great alti- 

 tudes, the surface of the plain is hard and the sand moves in crescentic 

 dunes as over a floor. These dunes may be seen from the railway in 

 traveling from Mollendo to Ariquipa and are one of th^ sights usually 

 remembered by the traveler. Mixed with the sand which drifts over 

 the southern coastal plains there is a large amount of white volcanic 

 ash or sand derived from volcanic materials. 



