2/0 GEOGRAPHY FROM AUGUSTUS TO TRAJAN. [CHAP.
viz. that the fish are found to congregate about the mouths of the
streams, where they are caught in great quantities. On the
other hand, the idea that the waters of the two refused to mingle
—which is found elsewhere with regard to rivers passing through
lakes—had its origin in the difference of colour which the stream
presents for some distance below the point where it enters. The
notion also that heavy substances can float on the surface of
the lake probably arose from its saltness and incrustations, cor-
responding as they do to the peculiarities of other pieces of water,
like the Dead Sea, where, as we have just seen, this takes place.
The story of the disappearance of the Tigris underground became
car famous, and is referred to by other authors. Thus
anceofthe Seneca says of it: "The Tigris is swallowed up
Tlgri8' and remains long out of sight, but at last emerges
at a far distant point, though there is no question about its
identity1." And Lucan writes:—
—Tigris sinking from the sight of day
Through subterranean channels cuts his way;
Then from a second fountain springs again,
Shoots swiftly on, and rushing seeks the main*.
Milton also would seem to have had the same idea in his mind,
when he made Satan enter Paradise—
Where Tigris, at the foot of Paradise,
Into a gulf shot underground, till part
Rose up a fountain by the tree of life8.
In the passage immediately following Pliny's account of the
Tigris which we have been considering, that author goes on to
say, on the authority of Claudius Caesar, that in the region of
Archene the Tigris flows so close to the Arsanias (i.e. the eastern
branch of the Euphrates), that when their streams are swollen
they flow together, yet without mingling their waters, for the
Arsanias, which is the lighter of the two, floats on the surface of
the Tigris for a distance of about four miles, and then separates
again from it, and falls into the Euphrates (i.e. the western
1 Sen., Nat, Quacst., 3. 26.
2 Lucan, Pharsal 3. 261—3 (Rowe's translation).
8 Par. Lost9 9. 71.