Hope . — The ‘ Sadd * of the Upper Nile. 513 
stream, sometimes carrying with them monster camoudies 
[Boa murina) or other snakes.’ Mr. Clarke caps this by telling 
how a rhinoceros was carried down a Bengal river to near 
Chittagong, and there caught and sent to the London Zoo- 
logical Gardens, where it was described as a new species by 
Mr. Sclater (R. lasiotis ). ‘ As these masses are caught by the 
sea-waves they are thrown back upon the beach, where they 
lie in great heaps until, dying, they go to help make up that 
extension of the coast-line which is continually driving back 
the waves to a greater distance. Sometimes a great tree, 
whose timber is light enough to float, gets entangled in the 
grass and becomes the nucleus of an immense raft, which is con- 
tinually increasing in size as it gathers up everything that comes 
floating down the river. The grass extends over the whole 
mass and mats it together until a formidable obstacle is 
produced ; but, notwithstanding all its efforts, the dam is 
imperfect. When eight or ten inches of rain fall in a day, 
and the river rises sixteen to twenty feet, the barrier must go. 
However (much) it may be attached to the bottom by a 
thousand anchors, it has to give way when the rise takes 
place, and here the hollow stems help in its destruction. By 
their great numbers they act as buoys, drag the great tangle 
of trees and bushes to the surface, unloose their own anchorage, 
until the mass sails away, ever on and on, to be broken in 
pieces and dashed on the shore, or perhaps carried far out 
to sea.’ 
It sometimes happens that a very obstinate obstruction 
succeeds in withstanding the flood, which by and by comes 
and deposits fresh masses of similar material on the fast- 
forming bank until it becomes an impenetrable barricade, 
narrowing the channel to a considerable extent. ‘ The waters 
become higher, and the current swifter. Something has to go, 
but it is not this late erection. The opposite bank is under- 
mined, one bush after another goes down with the flood, trees 
fall over and are also carried away, and a few months later the 
great river has a new bend. 5 And sometimes such an obstruc- 
tion is formed in the middle of the stream, in a shallow place. 
