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ancient kings to try）； but he found that the sea was higher than the
land。 So he first； and Darius afterwards； stopped making the canal；
lest the sea should mix with the river water and spoil it。 So it is
clear that all this part was once unbroken sea。 For the same reason
Libya…the country of Ammon…is； strangely enough； lower and hollower
than the land to the seaward of it。 For it is clear that a barrier
of silt was formed and after it lakes and dry land； but in course of
time the water that was left behind in the lakes dried up and is now
all gone。 Again the silting up of the lake Maeotis by the rivers has
advanced so much that the limit to the size of the ships which can now
sail into it to trade is much lower than it was sixty years ago。 Hence
it is easy to infer that it； too； like most lakes； was originally
produced by the rivers and that it must end by drying up entirely。
Again； this process of silting up causes a continuous current
through the Bosporus； and in this case we can directly observe the
nature of the process。 Whenever the current from the Asiatic shore
threw up a sandbank； there first formed a small lake behind it。
Later it dried up and a second sandbank formed in front of the first
and a second lake。 This process went on uniformly and without
interruption。 Now when this has been repeated often enough； in the
course of time the strait must become like a river； and in the end the
river itself must dry up。
So it is clear； since there will be no end to time and the world
is eternal； that neither the Tanais nor the Nile has always been
flowing； but that the region whence they flow was once dry： for
their effect may be fulfilled； but time cannot。 And this will be
equally true of all other rivers。 But if rivers come into existence
and perish and the same parts of the earth were not always moist；
the sea must needs change correspondingly。 And if the sea is always
advancing in one place and receding in another it is clear that the
same parts of the whole earth are not always either sea or land； but
that all this changes in course of time。
So we have explained that the same parts of the earth are not always
land or sea and why that is so： and also why some rivers are perennial
and others not。
Book II
1
LET us explain the nature of the sea and the reason why such a large
mass of water is salt and the way in which it originally came to be。
The old writers who invented theogonies say that the sea has
springs； for they want earth and sea to have foundations and roots
of their own。 Presumably they thought that this view was grander and
more impressive as implying that our earth was an important part of
the universe。 For they believed that the whole world had been built up
round our earth and for its sake； and that the earth was the most
important and primary part of it。 Others； wiser in human knowledge；
give an account of its origin。 At first； they say； the earth was
surrounded by moisture。 Then the sun began to dry it up； part of it
evaporated and is the cause of winds and the turnings back of the
sun and the moon； while the remainder forms the sea。 So the sea is
being dried up and is growing less； and will end by being some day
entirely dried up。 Others say that the sea is a kind of sweat exuded
by the earth when the sun heats it； and that this explains its
saltness： for all sweat is salt。 Others say that the saltness is due
to the earth。 Just as water strained through ashes becomes salt； so
the sea owes its saltness to the admixture of earth with similar
properties。
We must now consider the facts which prove that the sea cannot
possibly have springs。 The waters we find on the earth either flow
or are stationary。 All flowing water has springs。 （By a spring； as
we have explained above； we must not understand a source from which
waters are ladled as it were from a vessel； but a first point at which
the water which is continually forming and percolating gathers。）
Stationary water is either that which has collected and has been
left standing； marshy pools； for instance； and lakes； which differ
merely in size； or else it comes from springs。 In this case it is
always artificial； I mean as in the case of wells； otherwise the
spring would have to be above the outlet。 Hence the water from
fountains and rivers flows of itself； whereas wells need to be
worked artificially。 All the waters that exist belong to one or
other of these classes。
On the basis of this division we can sec that the sea cannot have
springs。 For it falls under neither of the two classes； it does not
flow and it is not artificial； whereas all water from springs must
belong to one or other of them。 Natural standing water from springs is
never found on such a large scale。
Again； there are several seas that have no communication with one
another at all。 The Red Sea； for instance； communicates but slightly
with the ocean outside the straits； and the Hyrcanian and Caspian seas
are distinct from this ocean and people dwell all round them。 Hence；
if these seas had had any springs anywhere they must have been
discovered。
It is true that in straits； where the land on either side
contracts an open sea into a small space； the sea appears to flow。 But
this is because it is swinging to and fro。 In the open sea this motion
is not observed； but where the land narrows and contracts the sea
the motion that was imperceptible in the open necessarily strikes
the attention。
The whole of the Mediterranean does actually flow。 The direction
of this flow is determined by the depth of the basins and by the
number of rivers。 Maeotis flows into Pontus and Pontus into the
Aegean。 After that the flow of the remaining seas is not so easy to
observe。 The current of Maeotis and Pontus is due to the number of
rivers （more rivers flow into the Euxine and Maeotis than into the
whole Mediterranean with its much larger basin）； and to their own
shallowness。 For we find the sea getting deeper and deeper。 Pontus
is deeper than Maeotis； the Aegean than Pontus； the Sicilian sea
than the Aegean； the Sardinian and Tyrrhenic being the deepest of all。
（Outside the pillars of Heracles the sea is shallow owing to the
mud； but calm； for it lies in a hollow。） We see； then； that just as
single rivers flow from mountains； so it is with the earth as a whole：
the greatest volume of water flows from the higher regions in the
north。 Their alluvium makes the northern seas shallow； while the outer
seas are deeper。 Some further evidence of the height of the northern
regions of the earth is afforded by the view of many of the ancient
meteorologists。 They believed that the sun did not pass below the
earth； but round i