434 Transactions. 



The rock structure is at once seen to be dominated by the development 

 of white sediments that appear to be limestones, though it is found on 

 a closer examination that many of these rocks are highly siliceous and that 

 they are associated with marls, mudstones, and sandstones. There are 

 also volcanic tuffs and lavas to a more restricted extent. The district has 

 been greatly disturbed by earth-movements, and the rock outcrops show 

 much folding, and probably faulting has taken place. There is also much 

 and rapid change in the direction of the strike of the rocks, which neces- 

 sarily greatly increases the difficulty of the stratigraphical problems. 



The only parts of the district that were closely examined were the follow- 

 ing : (1) Otamatea Arm from Komiti to one mile and a half above Batley ; 

 (2) Arapaoa Arm to one mile above Pahi ; (3) Pahi Arm ; (4) Oruawharo 

 Aria from Port Albert to Oneriri. (See fig. 1.) The information gained 

 from observations within this area cannot be regarded as in any way com- 

 plete, though some general conclusions were arrived at. It appears that 

 the lowest rock in the district examined is the limestone of the Gibraltar 

 Rocks, in the Pahi Arm. This was also Park's conclusion. This limestone 

 has often been correlated with the Whangarei limestone and with the 

 Waiomio limestone. In the last locality, near the Kawakawa coal-mine, in 

 the Bay of Islands, a bore showed that this type of limestone occurred very 

 nearly at the base of this younger series of rocks and certainly below the 

 hydraulic limestone.* Above this Whangarei limestone there is a series of 

 marls and mudstones which is perhaps 500 ft. thick, at any rate in the Pahi 

 Arm. Interstratified with the marls there are some bands of limestone 

 not very different from that of the Gibraltar Rocks, and, like it, containing 

 some glauconite. In places the glauconite forms thick beds of greensand, 

 especially in the Pahi neighbourhood. Locally this greensand appears to 

 give place to some very soft marly mudstones, which are of special import- 

 ance in the Otamatea Arm half a mile to the north-east of Batley, and on 

 the Arapaoa Arm two miles to the north-west of Batley. In the Pahi Arm 

 it appears that some Globigerina limestone, called generally ; ' hydraulic 

 limestone," occurs beneath the greensand, for it is in this material that 

 the bands of Whangarei limestone already mentioned are found. This 

 Globigerina limestone is highly arenaceous and contains a good deal 

 of glauconite, but in places it is siliceous. Occasionally this siliceous 

 character is shown in the presence of flinty bands, though typical rounded 

 flints are seldom found. 



The main mass of the " hydraulic " or Globigerina limestone is found 

 above the greensands. This relationship is particularly clear near Pahi, on 

 both the Arapaoa and the Pahi Arms. , The greater part of this limestone 

 is composed of broken tests of Globigerina (Plate XXXII, fig. 3), but in places 

 it contains a great number of sponge spicules and marine diatoms and radio- 

 laria (Plate XXXII, figs. 1, "2). This is markedly the case at the main bluff 

 at Batley and at Kaiwaka. In the upper part of this formation extremely 

 fine sediment makes its appearance and the organic contents dwindle. 

 The fine-grained sediment consists almost entirely of very minute grains of 

 quartz, well rounded, and seeming therefore to owe their transport to aeolian 

 influences rather than to those of water. This material forms the top of 

 the Batley Cliff, Paukihi, and also the whole of the cliff on the opposite 

 side of the Arapaoa Arm. On the foreshore of this cliff and farther to the 



* J. Hectoe, Progress Report, N.Z. Geol. Surv., 1892-93, 1894, p. xv, section A B„ 

 opp. p. xii. 



