ON THE RIVERS AND CREEKS. 181 



It happens sometimes also, though rarely, that 

 the obstruction takes place in the middle of the 

 stream. A very large tree is carried along and 

 deposited in a comparatively shallow place, where 

 it settles down and becomes the nucleus for a 

 deposit of debris and silt. Then the floating grass 

 anchors itself to some of the projecting branches, 

 and spreads all over until a little island is formed 

 Layer upon layer of mud is arrested at the upper 

 end until there is only a foot or two of water, and 

 on this bank some of the mocca-mocca roots, that 

 are continually coming down, get stranded and 

 commence to grow. A year or two after a dense 

 living palisade protects the small island, prevents 

 the silt from washing away, and helps to increase 

 the deposit by keeping a little still water behind. 

 Seeds come floating down in myriads, germinate 

 in the tangle, grow into great shrubs, and con- 

 tinually gather more mud and dtbris until the 

 little island lengthens down-stream to a consider- 

 able distance. The semicircle of gigantic arums 

 is sufficiently elastic to bend before the weight of 

 water ; the plants may be torn up by the roots, but 

 never broken off A thousand little eddies make 

 them tremble, and move backward and forward as 

 if alive, but still they go on producing one shoot 

 after another, and crowning all with their hand- 



