OF THE SEA, WHICH TO MANY FOOLS APPEARS TO BE HIGHER THAN THE EARTH
WHICH FORMS ITS SHORE.

_b d_ is a plain through which a river flows to the sea; this plain
ends at the sea, and since in fact the dry land that is uncovered is
not perfectly level--for, if it were, the river would have no
motion--as the river does move, this place is a slope rather than a
plain; hence this plain _d b_ so ends where the sphere of water
begins that if it were extended in a continuous line to _b a_ it
would go down beneath the sea, whence it follows that the sea _a c
b_ looks higher than the dry land.

Obviously no portions of dry land left uncovered by water can ever
be lower than the surface of the watery sphere.