588 PERU. 
rains at Lima, though dense dripping mists are not unfrequent; and 
this aridity of climate is still more remarkable to the south over the 
province of Atacama, which is a perfect desert. We have already 
alluded to the cause of this dryness ;* and we perceive from it, that 
the Andes have, to a great extent, protected the lands to the eastward 
from the fate that has befallen Africa, besides supplying from their 
snows a great number of streams. This chain, therefore, though 
many a city may have been laid waste by the earthquakes and erup- 
tions it has engendered, is a blessing and not a curse to the continent. 
RECENT DEPOSITS OF THE COAST. 
In the cliff south of Callao, the geological constitution of the plain 
above is finely exposed to view. This cliff varies in height from forty- 
five to sixty feet. On measurement with a line at one place, it was 
found by the writer to be forty-eight feet high, which is hardly below 
the average elevation. 
The material of the cliff consists of layers of sand, more or less 
argillaceous, alternating with others of an impure clay, and others of 
coarse pebbles. None of it is indurated into a coherent rock. The 
lowest layer is a bed of coarse gravel, with rounded stones often eight 
or ten inches in diameter. The pebbles are identical in character 
with those now forming the beach, being rolled fragments of the 
various rocks of the mountain. Above this, the layers are mostly of 
sand or clay, though sometimes pebbly. 
The first above the lowest is argillaceous; and generally yellow or 
ochreous in colour, varying to a reddish or purplish tint. It contains, 
especially in its lower part, large stumps and branches of an exoge- 
nous tree, the wood of which is soft and mostly blackened, though 
not carbonized. ‘The largest mass of wood observed was two feet in 
diameter, and several were six feet long. Others were mere twigs. 
The branches were commonly flattened, from pressure, to a thickness 
but a third or a fourth of the breadth. They lay scattered through 
the clay without any regularity ; and neither roots nor leaves were ob- 
served with them. ‘The fragments are so small, in some places, that 
they give the clay a mottled appearance when broken. 
The same layer is penetrated with irregular cylindrical stems, 
resembling twigs of different sizes, from an eighth of an inch to an 
inch in diameter, though generally ranging between a fourth and half 
* Page 455, 
