﻿334 Transactions — Geology. 



Above tlie loam a vegetable soil moi-e or less darkly coloured by humus, 

 and from to 4 feet in thickness is generally found. This soil sometimes 

 rests abruptly on the loam biit more often passes gradually down into it. It 

 contains in various places, and at various depths down to 18 inches from the 

 surface, collections of marine pipi-shells {Mesodesmachem,nitzii)sin.(\.\)\\\:\it\vood, 

 evidently the remains of Maori feasts, for they still occasionally bring up these 

 shells from the mouth of the river. No trace of holes having been dug for 

 Maori ovens can be seen, althoiigh if any digging or tiirning over of the soil had 

 taken place it could not fail to be detected in the clean sections of the river 

 bank. We must therefore conclude that these remains show the level of the 

 river bank at the time when the shells were cooked. The ordinary floods of 

 the Waikato seldom overflow the banks of the river, although they fill up large 

 swamps beyond the banks ; and even when they do flow over they seldom 

 remain at that height more than three or four days, and they deposit very 

 little mud during that time ; but in August and September of last year a 

 heavy flood occurred, which wa,s the highest that had been known for 30 years, 

 and it covered the banks for about three weeks. During this time a layer of 

 fine yellow loam about three quarters of an inch thick was deposited, but the 

 traffic on the bank destroyed a good deal of it again. Of course when the 

 banks were lower the floods would be oftener, and perhaps remain longer, but 

 I think that an inch of deposit in 20 years would be a very liberal allowance, 

 and at this rate some of the Maori feasts would date back 360 years. The 

 next series of beds, in descending order, is the clays and sands which form the 

 greater part of the hills between Rangiriri and Mere-mere, and on the opposite 

 side of the river ; this also contains no fossil shells, bu.t only plants and beds 

 of lignite with wood, and it is pi-obably of fresh water origin also. There 

 appears therefore to be no geological evidence of the sea having been in the 

 Lower Waikato valley since the upheaval of the Waitemata series ; that is 

 since it has had any existence. I therefore think that the fact of the presence 

 of several littoral plants in the Lower Waikato basin, brought forward last 

 year by Mr. Kirk,* may be best explained by supposing that they have spread 

 down the river from the Middle Waikato basin after the formation of the 

 Taupiri gorge. 



It is, I believe, the commonly received opinion that islands in a river have 

 generally been caused by the stream gradually cutting through its bank at a 

 sharp bend, and leaving what was before a point as an island. Without 

 committing myself to the opinion that this is never the case, I may state that 

 it is seldom, if ever, the way in which islands are formed. If it were so, we 

 ought to see rivers running round a deep re-entering bend without a salient 

 point projecting into it, and islands ought often to be shoi-ter in the direction 

 * See Trans. K Z. Inst., Vol. III., p. 147. 



