Geoscience Reference
In-Depth Information
Figure 5.2. Siliceous megascleres in sponge pottery, lower White Nile Valley. (SEM
Photo: Don Adamson.)
travelled and of the natural history of the regions they visited. They also received
information from the Arab traders they encountered about likely sources of water
(
Figure 5.4
).
From these and other accounts, it is possible to glean useful information about the
historical incidence of floods, droughts and famines in this vast region (Nicholson,
1976
; Nicholson,
1978
; Nicholson,
1980
), a topic discussed in
Chapter 23
.Ina
remote library in the small desert town of Chinguetti set amidst the dunes of inland
Mauritania, there are records of past climatic events written by Arab scholars on
vellum that extend back 1,000 years but which have yet to be studied in detail. Many
of the older rolls of vellum are abraded. When the author asked why, the custodian
said with pride but rather sadly that they had been hurriedly stuffed into saddlebags
by his ancestors and taken off into the desert on racing camels for safekeeping during
raids from marauding bands over the past 1,000 years.
The maintenance of accurate written records of when certain plants blossomed
enabled the Chinese meteorologist Chu Ko-Chen (
1973
) to use such phenological
evidence to reconstruct a temperature history for China covering the last 3,500 years -
a remarkable achievement. We are also fortunate in having a detailed annual record
of wet and dry years in China for the past five centuries (Anon.,
1981
). Time series
analysis of this outstanding archive has shown that drought years in eastern China
were generally coeval with droughts in India and with years of low flow in the Nile
