INLAND SAND PLAINS. 603 
ingly covered with sand. If a hillock chain somewhat distant 
from the sea extends in a line parallel with the Andes, namely, 
from 8. 8S. E. to N. N. W., the western declivity is almost en- 
tirely free of sand, as it is driven to the plain below by the 
south-east wind, which constantly alternates with the wind from 
the south.” * 
It is difficult to reconcile this description with that of Meyen, 
but if confidence is to be reposed in the accuracy of either 
observer, the formation of the sand-hills in question must be 
governed by very different laws from those which determine 
the structure of coast dunes. Captain Gilliss, of the American 
navy, found the sand-hills of the Peruvian desert to be in 
general crescent-shaped, as described by Meyen, and a similar 
structure is said to characterize the inland dunes of the Llano 
Estacado and other plateaus of the North American desert, 
though these latter are of greater height and other dimensions 
than those described by Meyen. There is no very obvious 
explanation of this difference in form between maritime and 
inland sand-hills, and the subject merits investigation. It is, 
however, probable that the great mobility of the flying dunes 
of the Peruvian desert is an effect of their dryness, no rain 
falling in that desert, and of the want of salt or other binding 
material to hold their particles together. 
Inland Sand Plains. 
The inland sand plains of Europe are either derived from 
the drifting of dunes or other beach sands, or consist of dilu- 
vial deposits, or are ancient sea-beds uplifted by geological 
upheaval. As we have seen, when once the interior of a dune 
is laid open to the wind, its contents are soon scattered far and 
wide over the adjacent country, and the beach sands, no longer 
checked by the rampart which nature had constrained them to 
build against their own encroachments, are also carried to con- 
siderable distances from the coast. Few regions have suffered 
* Travels in Peru, New York, 1848, chap. ix. 
