Meteorology   

for a certain time, and then dry up and grow old, while other parts in

their turn are filled with life and moisture. Now when places become

drier the springs necessarily give out, and when this happens the

rivers first decrease in size and then finally become dry; and when

rivers change and disappear in one part and come into existence

correspondingly in another, the sea must needs be affected.

If the sea was once pushed out by rivers and encroached upon the

land anywhere, it necessarily leaves that place dry when it recedes;

again, if the dry land has encroached on the sea at all by a process

of silting set up by the rivers when at their full, the time must come

when this place will be flooded again.

But the whole vital process of the earth takes place so gradually

and in periods of time which are so immense compared with the length

of our life, that these changes are not observed, and before their

course can be recorded from beginning to end whole nations perish

and are destroyed. Of such destructions the most utter and sudden

are due to wars; but pestilence or famine cause them too. Famines,

again, are either sudden and severe or else gradual. In the latter

case the disappearance of a nation is not noticed because some leave

the country while others remain; and this goes on until the land is

unable to maintain any inhabitants at all. So a long period of time is

likely to elapse from the first departure to the last, and no one

remembers and the lapse of time destroys all record even before the

last inhabitants have disappeared. In the same way a nation must be

supposed to lose account of the time when it first settled in a land

that was changing from a marshy and watery state and becoming dry.

Here, too, the change is gradual and lasts a long time and men do

not remember who came first, or when, or what the land was like when

they came. This has been the case with Egypt. Here it is obvious

that the land is continually getting drier and that the whole

country is a deposit of the river Nile. But because the neighbouring

peoples settled in the land gradually as the marshes dried, the