440 Transactions. 



Arm, south-west shore, opposite Pahi, at Coates's Landing ; (3) Pahi Aim, 

 opposite Pahi Township, near Jackman's. The greensand at these three- 

 places is clearly seen to lie below the main mass of the hydraulic limestone. 

 Farther south the glauconitic nature of these sandstones seems to decrease 

 and the brown sandstone next described takes its place. 



These brown sandstones are of considerable thickness on the north side 

 of the Arapaoa Arm at a prominent point two miles below Pahi. These 

 sands contain very little glauconite, but, like the greensands, they are 

 strongly concretionary. Amongst the concretions there are a few small 

 ones of siderite. No fossils were found in any of the concretions in this 

 brown sand. Near Batley this brown sand is exposed near the Maori settle- 

 ment of Mateanui. It certainly lies below the ammonite beds in this 

 locality, and appears to be separated from them by a bed of very siliceous 

 hydraulic limestone. 



Barite occurs from time to time in this rock series at various horizons. 

 Near Kaiwaka it has been found lying on the surface of the hydraulic lime- 

 stone. A large concretion was found at the point B near Colbeck's Land- 

 ing, and another was found in the ammonite beds on the north side of the 

 Arapaoa Arm close to Pahi. It is, of course, a fact that concretions of 

 barite have been found in some ocean dredgings. It is thought that the 

 greensands, brown sand, and ammonite beds are practically the same horizon. 

 It is certainly true that the ammonite beds are not older than the green- 

 sands, for near Batley there is a large angular boulder of greensand em- 

 bedded in the ammonite beds. The angular nature of this boulder shows 

 that it has been transported a very short distance, a consideration that 

 is emphasized by the incoherent nature of the greensand, which does not 

 bear transport. The boulder almost gives the impression of being merely 

 a local phase of the ammonite marls. In the same ammonite beds there 

 are many concretions that have the appearance of those that are so common 

 in the greensands. Thus the impression is formed that the ammonite beds 

 and the greensands are different local phases of the same formation. 



Hydraulic Limestone. 



This name has been used for a number of strata that have a general 

 similarity in appearance, though in composition they prove to be widely 

 different. The name " hydraulic limestone " has apparently been applied 

 to them under the impression that they are so constituted that they can 

 readily be converted into hydraulic cement. This may actually be true 

 with reference to a small portion of the strata known under this name, but 

 it is wholly misleading with reference to the greater part of the formation. 

 In the Pahi section, for instance, hydraulic limestones are represented 

 by Park over the greater part of the distance between McMurdo's and 

 Colbeck's Landing (loc. cit., 1887, p. 222, and section). The Batley Heads are 

 also said to be composed of hydraulic limestone (loc. cit., p. 229). A micro- 

 scopic examination of these materials shows that the external similarity of 

 the rocks actually conceals great differences in composition and structure. 



In the Pahi Arm the beds near Colbeck's Landing are mudstones and 

 sandstones almost destitute of calcareous matter. At Awakino the material 

 is a Globigerina limestone, but it contains a large amount of glauconite, 

 quartz, and other impurities. At Batley the small bluff near the wharf 

 is a glauconitic limestone, but the material of the main bluff, Paukihi, is 

 almost wholly siliceous. Near the base it is very white and compact, but 

 shows no organisms when examined under the microscope. In many places 



