460 Transactions. — Geology. 



will show this. Near the surface the borings invariably 

 passed through soft clay or mud, after which the material met 

 with always contained more or less sand. To attribute to the 

 agency of the river the whole of the material passed through 

 in the Tokatoka Swamp borings would be to demand a con- 

 tinuance of conditions under which a gradual subsidence took 

 place with sufficient slowness to enable the river to fill up the 

 depression. This appears to be highly improbable; there is 

 nothing to warrant the supposition, which, moreover, is not 

 required to explain existing conditions. The great depth of 

 river-deposit at Mangawhare (80ft.) is a more difficult matter 

 to account for, and until further evidence is forthcoming we 

 may attribute it to some local depression. 



It is difficult to arrive at any accurate knowledge as to the 

 rate at which the deposit was laid down. As affording some 

 guide to this it may be mentioned that two clubs of black-maire 

 [Olea cunningliamii) — the kind used by the natives in crush- 

 ing fern-root — were found about 13 ft. from the surface by 

 some men whilst cutting a drain. It is not at all likely that 

 these clubs were buried to that depth by the natives ; it is 

 much more probable that they were dropped into the waters 

 of the old swamp or harbour and were gradually covered up. 

 The wood of which they were made would at once sink to the 

 bottom. This is very slender evidence to build on, but if it is 

 to be accepted at all it would go to show that the deposit has 

 been a rapid one, and that the last 13 ft. have been laid down 

 within a period which could not have extended over many 

 generations. 



The borings at Mangawhare appear to have gone through 

 nothing but river-mud before reaching fairly hard argillaceous 

 limestone, a rock similar to that which outcrops at Aranohue, 

 Okahu, and other places along the eastern side of the river. The 

 age of this limestone is considerably greater than that of the 

 river-deposit, so it may here be taken as the basement rock. 

 Hence at Mangawhare the depth of alluvium is about 80 ft. ; 

 and, as no remains of marine organisms are louml, we may 

 conclude tliat the deposit is of fluviatile origin. This no doubt 

 applies to all of the material forming alluvial fiats along the 

 river north of Te Kopuru. It is not improbable ttiat the sea 

 once flowed over the land now known as the Tatarariki Flat, 

 and that the high ground from Te Kopuru south at one time 

 formed part of the western shore-line of the harbour. 



; Oil the eastern bank of the river there occur some very 

 remarkable volcanic outcrops, rising through the sedimentary 

 rocks at short intervals and extending for several miles in a 

 line running approximately nortli and south. The first of 

 these met with is at Maungaraho, evidently the remains of a 

 huge dyke 720 ft. in height and dipping towards the north- 



