Marshall. — Geology of the Central Kaipara. 439 



small outcrop of compact limestone. This rock consists almost solely of 

 Globigerina. In the large bluff of hydraulic limestone at D there are three 

 distinct hard bands of polyzoal limestone. The most northerly of these 

 bands is mainly polyzoal, but there are numerous Foraminifera, including 

 Amphistegina, Rotalia, Cristellaria, and Textularia, with some Globigerina. 

 There are a few echinoderm fragments and much Lithothamnium. Of 

 inorganic material there is a good deal of glauconite and a little quartz. 

 The middle hard band 120 yards distant consists mainly of small Foramini- 

 fera, especially Globigerina, and a small Rotalia. There are only a few 

 echinoid and polyzoan remains. Glauconite and quartz are in relatively 

 large quantity. The southern band of this limestone consists mainly of 

 Polyzoa. There are many echinoid plates and Foraminifera, amongst them 

 Amphistegina, Globigerina, Textularia, Rotalia, and Carpenteria. There is a 

 good deal of glauconite and of brown micaceous matter and small grains of 

 quartz. There are also round grains of brown volcanic glass. The hydraulic 

 limestone in which these bands are stratified consists mainly of Globigerina. 

 Calcified sponge spicules are numerous. There are no other organic remains, 

 but much glauconite, brown mica, and quartz. 



Ammonite Beds. 



These are mainly formed of a fine muddy substance of a peculiarly 

 unctuous nature. It has a dark-brown colour, and its incoherence allows 

 it to slip easily, and it therefore presents extremely poor exposures. Thus 

 near Batley and to the south-east of Pahi, where these beds outcrop, the 

 hillside is gradually slipping into the harbour, and well-developed outcrops 

 are exceedingly hard to find. At a third locality on the north, side of the 

 Arapaoa Arm, about two miles from Batley, the mateiial is more stable, 

 though even here the hillside is gradually slipping downwards. 



These beds contain a large number of concretions. Usually the con- 

 cretions are merely portions of the country that contain a higher percentage 

 of carbonate of lime. Microscopical examination shows that they consist 

 mainly of fine quartz sand cemented with calcareous matter. There is a 

 little glauconite, and much brown matter, apparently of vegetable origin. 

 Some of these concretions are composed wholly of pisolitic spherules 2-5 mm. 

 in diameter. The pisolites are composed of radiating crystals of calcite. 

 The concretions are of very different shapes and of varying size, though 

 few of them are more than 1 ft. in diameter. Cone-in-cone structure is often 

 associated with them in all the localities where the beds outcrop. Near 

 Batley the beds contain concretions which are far more glauconitic than 

 elsewhere. I am at present wholly unable to give a satisfactory explanation 

 of the origin and formation of these concretions. 



Greensands. 



These are best developed at Pahi and to the north-west of that township 

 along the shore of the Arapaoa Arm. The sands are in places almost pure 

 glauconite, but they appear to have been deposited in relatively shallow 

 water, for at places they are finely conglomeratic. They contain many 

 concretions the exterior of which has been largely converted into limonite. 

 Several of these concretions near Pahi enclose a large variety of molluscan 

 fossils, and in one of them Mr. J. A. Bartrum found a reptilian bone. The 

 concretionary matter that contains fossils is particularly abundant at three 

 localities — (1) Arapaoa Arm, on the north-east shore near Pahi ; (2) Arapaoa 



