DIVERSION OF RIVERS. 497 
the channels of the mountain sources of important streams, and 
the Arabs executed immense works of similar description, both 
in the great Arabian peninsula and in all the provinces of Spain 
which had the good fortune to fall under their sway. The 
Spaniards of the fifteenth and sixteenth centuries, who, in many 
points of true civilization and culture, were far inferior to the 
races they subdued, wantonly destroyed these noble monuments 
of social and political wisdom, or suffered them to perish, be- 
cause they were too ignorant to appreciate their value, or too 
unskilful as practical engineers to be able to maintain them, 
and some of their most important territories were soon reduced 
to sterility and poverty in consequence. 
Diversion of Livers. 
Another method of preventing or diminishing the evils of 
inundation by torrents and mountain rivers, analogous to that 
employed for the drainage of lakes, consists in the permanent 
or occasional diversion of their surplus waters, or of their entire 
currents, from their natural courses, by tunnels or open chan- 
nels cut through their banks. Nature, in many cases, resorts 
to a similar process. Most great rivers divide themselves into 
several arms in their lower course, and enter the sea by differ- 
ent mouths. There are also cases where rivers send. off. lateral 
branches to convey a part of their waters into the channel of 
other streams.* The most remarkable of these is the junction 
between the Amazon and the Orinoco by the natural canal of 
the Cassiquiare and the Rio Negro. In India, the: Cambodja 
and the Menam are connected by the Anam; the Saluen and 
the Irawaddi by the Panlaun. There are similar examples, 
* Some geographical writers apply the term difurcation exclusively to this 
intercommunication of rivers; others, with more etymological propriety, use 
it to express the division of great rivers into branches at the head of their 
deltas. A technical word is wanting to designate the phenomenon mentioned 
in the text, and there is no valid objection to the employment of the anatomi- 
cal term anastomosis for this purpose. 
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