PHYSICAL GEOGRAPHY. [CHAP.
one of the first necessaries of existence, and thus determining the
localities fitted for the abode of man. In consequence of this
they have attracted attention in all ages, and among the Greeks,
as soon as speculation on the phenomena of nature arose, we meet
with interesting observations both on the general characteristics of
rivers and on their more marked peculiarities. Aristotle first
pointed out that almost all large rivers take their
rise *n 2reat mounta^n ranSes—a statement which
he illustrates by instances taken from all the three
continents; and he compares the elevated portions of the globe
to a vast sponge, which retains the water that falls in rain, and
after a while sends it forth again from numerous sources1. Another
feature by which he was attracted was the disappear-
ance °f rivers» an(* *e^r Pursu*ng a subterraneous
course, of which he gives the following account.
"That there are such chasms and openings in the ground is clear
from the rivers that are engulfed. Now this happens in many
parts of the earth, as, for instance, in Peloponnesus, where there
are several instances in the neighbourhood of Arcadia. The
reason is that, whereas that is a mountain district, it has no
channels leading from the depressions of the ground to the sea.
For when an area is filled and has no outflow, it finds for itself a
passage vertically, by the force of the water that presses from
above2." The places in Arcadia here referred to are the valleys
which contain the lakes of Pheneus and Stymphalus, and the phe-
nomena of both of these are accurately described by Eratosthenes,
who says that the river of Pheneus finds its way into a passage, or
"strainer," as he calls it, and that when this is closed the valley
becomes a lake; but when it opens the waters sink, and the river
Ladon, with which it communicates underground, is flooded The
same thing happens to the lake of Stymphalus, the stream from
which forms the river Erasmus in the Argive territory8. A further
point, to which Polybius draws attention in his
Erosion, description of the site of Psophis in the Pelopon-
nese, is the action of a river in hollowing out a
1 Ar., MeteoroL, i.13. n—*«.
8 fltid., 1.13, 27, 28.
8 EratostL ap. Strabon., 8. 8.4.