490 Transactions. — Geology. 



distinctly volcanic, with, occasionally, fragments of scoria as 

 large as a pea. 



The position of the Wairau tuffs appears to be above the 

 Cheltenham breccia and below the Orakei greensand. I am 

 uncertain whether they are above or below the Ponsonby tuff, 

 since they seem everywhere to be above it ; but at Ponsonby, 

 where the section is clear, either they are not above it or thev 

 must be more than 100 ft. above it, a most unusual position. ' 



The group of tuffs is more sandy than the Parnell grit, but 

 the scoria can easily be seen with a lens. At the Wairau 

 Creek I discovered a fragmentary Gastropod shell near the 

 base of the second bed. It is very minute, not as large as a 

 pea, and several whorls are evidently missing ; but I believe it 

 is a species of Littoriua. Elsewhere I have not been able to 

 detect any fossils. 



Since there are no fossils, it will be advisable to give the 

 reasons for identifying volcanic beds at Howick, St. John's 

 College, the Tamaki, and Manukau Harbour, with this bed at 

 the Wairau. In the first place, the beds do not resemble 

 the ordinary Waitemata sandstones, which are blue or grey, 

 while these tuffs are brown or black, with a tendency some- 

 times to spheroidal weathering. In the second place, al- 

 though there is a little scoria present occasionally in other 

 beds, it is never so abundant. In these beds, too, occur veins 

 of calcite, with large crystals sometimes -Jin. long (dog-tooth 

 spar) ; and there are also veins of zeolites. And, moreover, 

 these beds always occur as a well-defined group of black 

 bands in the cliff, the lower being the more tufaceous. 



At the north head of Castor-oil Bay the tuffs are separated 

 by bands of sandstone, as at St. John's College. Generally 

 they are separated by thinner layers of shale. 



In the first section I observed the bed was about 8 ft. 

 thick. Across Castor-oil Bay no section can be seen, the 

 ground being low. In the floor of the bay nothing can be 

 seen, owing to the covering of yellow sand. If there is no 

 break — and there is no reason to suppose one — the Wairau 

 tuff's are here about 30 ft. above the Cheltenham breccia. 



To the north of the Wairau (Castor-oil Bay) I saw nothing 

 of the tuffs, but some of the finer tuffs at' Whangaparaoa 

 resemble them. 



On the southern side of the harbour there is no outcrop of 

 the tuffs until St. John's College is reached, the reason being 

 that younger beds occur along the cliffs. At St. John's Col- 

 lege they are seen in the floor of the stream when the tide is 

 out and a freshet has scoured away the mud. The bed of the 

 stream is obscured farther up by a raupo swamp, and the hill- 

 sides are thickly covered with gorse. Wherever the strata 

 can be seen they are, however, sandstones, so that it seems 



