112 NATURAL SCIENCE. .,,^„, 



Barito, which flows towards the soutli, tlie Kapuas to the west, the 

 Rejang to the north, and the Alahakkani to tlie east. The Barito is 

 570 miles long, according to Schwaner. Besides these large rivers, 

 there is a great number of smaller streams, which rise in the 

 different mountain chains. 



The rivers of Borneo pass through three distinct phases in 

 their passage from the mountains to the sea. In an iippe/ course they 

 rush over a rocky bed with cataracts and rapidly shifting pebble 

 islands. The middle course is through a more level country, in which 

 the stream is often replaced by a string of lakes. The extent of these 

 lakes depends on the time of year ; during the rainy season the 

 surrounding forests are often flooded for miles, while in the dry season 

 they partially dry up, leaving a black fertile land, dotted with small 

 patches of water. Such, for instance, is the case in the rivers 

 Barito and Kapuas, both of which have an extended lake district. 

 Another feature of this part of the course is the formation of natural 

 canals (aiitassan) which cut across the loops. Similar natural canals 

 (irussan) connect neighbouring rivers with one another. They are 

 formed by the floods that arise during the west monsoon, and are 

 very serviceable as water-routes to the traveller. 



In the lower course, the river winds slowly through a flat swampy 

 country, fringed with mangroves, nipa-palms, and other tangled jungle 

 growth. This lagoon district is inundated daily at high water, and 

 is covered for months during the rains. On retreating, the subsiding 

 waters leave behind a black mud, rich in humus and full of shells. 

 A large amount of this mud is brought down by the rivers. Its 

 accumulation causes the formation of numerous mud islands. Occa- 

 sionally the accumulation takes place in such a manner as to form a 

 natural embankment, through which the river flows at a higher level 

 than the surrounding marsh-land. A part of the sediment is carried 

 out to sea, where it is deposited in banks which often constitute 

 dangerous bars across the mouths of the rivers. On the east coast 

 there are mud banks extending for 8 — 10 nautical miles into the sea : 

 even at a distance of 10 miles the sounding line only gives a depth 

 of 33 feet. 



The deposition of sedimentary material brought down by the 

 rivers, protected in some cases by the presence of coral-reefs, causes 

 a rapid extension of the coast. This is aided by the growth of the 

 jungle vegetation. On the newly-formed marsh-land mangroves soon 

 spring up, and by their pcaident air-roots favour the accumulation of 

 the mud. The forward movement of the mangrove woods has been 

 estimated to amount to be more than a hundred metres in forty years. 

 Another jungle tree which acts in a similar manner is the nipa- 

 palm. Flourishing alike in salt or fresh water, its matted roots serve 

 admirably to retain the flotsam of the rivers ; and it is propagated 

 rapidly by its angular fruit, which, on falling, sinks easily into the soft 

 mud. On the coast of Sarawak the annual increase is estimated at 



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