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 Cafiete 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 with 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 great 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 Ica and Pisco; also some smaller ones to the west 
of Ica 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 the 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, 
