Walsh.--A'//Vv7.s- of Dixit piH'ara an of the New Zealand Bush. 443 



the view of protecting them against the scour of the current But the 

 scheme generally defeats its own object, and is often the cause of much 

 mischief, which, moreover, is not always confined to the locality in which 

 the planting takes place. Sooner or later, especially if the river is a rapid 

 one, and runs through alluvial country, the trees are undermined and swept 

 down until they are caught by some obstruction or are stranded in some 

 shallow place. Here they intercept the silt and the floating debris that 

 comes down with every flood, and an island or dam is formed, which drives 

 the current into the banks, or even compels it to seek a new channel. In 

 the Lower Waikato the obstruction of the willow islands has caused the 

 lied of the river to silt up to such an extent that in many places the level 

 land on the banks is flooded every winter, and the Township of Mercer is 

 frequently under water after a few days' heavy rain. 



It may be asked whether the damage done by the willow-trees has any- 

 thing to do with the subject of this paper, which professes to deal with 

 the effect of the disappearance of the forest. The answer is that if the 

 forest had not been removed the damage done by the willows would be 

 comparatively trifling — if, indeed, it would have been considered necessary 

 to plant them. But, as I have endeavoured to show, it is the removal 

 of the forest that is directly responsible for the growing violence of the 

 floods, and therefore for the increasing amount of silt and floating detritus, 

 wliich the willows intercept. 



There is another aspect of the silting question that must not be over- 

 looked — ^viz., the formation of river-bars and the silting-up of harbours. 

 All the mineral debris, stones, gravel, and mud that are carried down by 

 a stream are immediately deposited on the bottom as soon as the current 

 ceases to act, which it does on reaching the sea, and here it forms a bank 

 or shoal, which is augmented by the sand or other material which the sea 

 washes on to it. If the river falls into landlocked water the finer particles 

 held in suspension are carried out into the stream, and drift up and down 

 with the tide until they are precipitated wherever there is least current. 

 In many river-mouths, estuaries, and harbours the effect of the wholesale 

 forest -clearing is already being severely felt. Of late years, unless where 

 temporarily scoured out by a fresh, there is less water on many of the bars, 

 while in some of the shallower harbours— e.g., those of the Thames, Coro- 

 mandel, &c.- — ^the wharves have had to be lengthened and the buoys on the 

 shoals moved further out. One of the most fertile sources of harbour-silt, 

 and one not generally taken notice of, is the fine dust that is formed by 

 the action of the sun on the bare hills, and washed by the rain into the 

 creeks. This is, doubtless, one of the principal factors of the extensive 

 mud-flats so frequently found in landlocked waters. 



~ (3.) Drying-up of Streams. 



So far I have dealt only with the evils caused by water in excess ; but 

 it can also be shown that the removal of the forest involves trouble in the 

 opposite direction — viz., in the diminutiojti of the supply when it is moet 

 needed. 



The volume of a stream is derived from two sources — the first consist- 

 ing of the water that flows directly ofi the surface, and the second of that 

 which comes through the ground. Both of these, of course, are originally 

 supplied by the rain. 



