﻿HuTTON. — On the Alluvial Deposits of the Lower Waikato. 335 



of the river than across it, and these cases are certainly rare, if indeed they 

 exist at all The river also shonld always swell out round an island, whereas 

 islands are often seen in parts of a river where it is no broader than it is either 

 above or below it ; and it would also be difficult in this way to account for two 

 islands lying pai-allel and abreast of one another — ^a case of common occurrence, 

 especially near the mouths of rivers. Besides, the greatest strength of the 

 current is never in the bends. A sharp bend blocks up the stream, and 

 reduces its velocity ; and it is at the point where the water is able to get away 

 that the strongest current is found. Any one who has been used to paddling 

 up a river in a canoe will, I am sure, bear me out in this. The wear on the 

 bank therefore is greatest at the point and gets less and less towards the bend, 

 and the river tends to wash away the point and not to detach it as an island. 

 The great flood of last August, which has been already mentioned, has left 

 behind it two sand-banks which bid fair to become permanent islands, and 

 which well exemplify the usual way in which these islands are formed. The 

 sand-banks of the Waikato are constantly shifting their places, and moving 

 down the stream, on account of the sand being pushed along the bottom of the 

 river. This only happens when they are covered by water, for when the river 

 is low, and the banks are above it, the strength of the current is not sufficient 

 to wash them away, and they retain their position until the next flood. 

 The high flood of last spring raised two of these banks — one opposite to 

 Rangiriri and the other about four miles above it, opposite to Armitage's 

 farm — so high that no subsequent flood covered them until the beginning of 

 April, 1871, so that they were about seven months in the spring and summer 

 above water. During this time they became so covered with vegetation that 

 the flood of last April, which covered them, had no further eflfect than to raise 

 them still higher by depositing more sand and mud round the plants, and it is 

 evident that if this is continued they will soon only be covered by the highest 

 floods, and will thus resemble the ordinary islands of the river. 



I visited the island opposite to Rangiriri on the 17th of last April, and 

 collected on it the following plants : — Nastzirtiujn pcdustre^ abundant ; Pelar- 

 gonium clanclestinum, common ; Geranium mierophyllum ; Trifolittm 2>ratense \ 

 T. minus ; Coprosma robusta, one seedling ; Cotula Goronopifolia, abundant ; 

 Erigeron canadense, abundant ; Gnajjhalium luteo-alhum ; G. involucratum ; 

 Sonchus oleraceus ; Plantago major, abundant ; Rumex oUusifolius, abundant ; 

 Juncus communis ; Cijperus ustulatus ; Lsolepis setosus ; Agrostis ceraida, 

 common ; Arundo conspicua, one old plant only which had been floated down 

 the river, but was now standing upright and growing well ; IIolcus mollis ; 

 Agrostis Billardieri, and Poa australis v. Icevis. 



This island was then about 250 yards long by 50 broad, the highest i:)oint 

 being the end pointing down the river, as is always the case with sand-banks. 



