Marshall. — Geology of the Central Kaipara. 441 



the hydraulic limestone is highly siliceous, and in places it is distinctly 

 flinty. No organisms have been recognized in these flinty types. It cannot 

 at present be definitely stated whether the flinty type occurs only at one 

 definite horizon or whether there are several different flinty strata. A 

 little higher up the cliff the rock consists mainly of Globigerina tests, but 

 it also contains a great variety of diatom* and radiolarian remains, with an 

 abundance of sponge spicules. In the rock from the upper part of the cliff 

 no organic remains could be distinguished, and the rock is merely a white 

 mudstone that consists almost entirely of very minute rounded particles of 

 quartz. 



On the north-west side of the Arapaoa Arm, near Pakaurangi Point, 

 this series of rocks is continued. The continuation has already been de- 

 scribed in demonstration of the fact that the unconformity described by 

 Park between his chalk marls (actually white mudstones above the hydraulic 

 limestone) and his Komiti Point beds (here called " Pakaurangi Point beds ") 

 does not in reality exist. It is only necessary to repeat here that the white 

 mudstones become dark-coloured and are finally succeeded by the tufaceous 

 Pakaurangi Point beds without any sign of erosion. 



Pakaurangi (Komiti) Point Beds. 



These are moderately coarse sandy beds mainly composed of material 

 of volcanic origin, and are therefore rightly described by Hector as tufa- 

 ceous. As the beds are followed farther westward and southward the 

 material becomes coarser and the sediments are in places breccia or con- 

 glomerate beds. The upper beds at the apex of Pakaurangi Point still have 

 a species of Amphistegina and a great abundance of Miogypsina aff. irregu- 

 laris (Orbitoides of Park), and is probably of Lower Miocene age. 



It is well known that flint-beds are associated with the fine-grained 

 Globigerina limestone — the so-called Amuri limestone of North Canterbury 

 and Marlborough. An account of these has just been published by 

 Thomson. In his article he states that " The absence of such skeletons 

 [Radiolaria, sponges, and diatoms] in any of the numerous microscopic 

 sections examined removes any ground for accepting such an explanation 

 [organic source] for the origin of the silica in the present case. ... In 

 view of the widespread occurrence of the flint -beds, apparently at a definite 

 horizon, the theory of original deposition [chemical precipitate] seems most 

 acceptable, "f 



In a paper published last year I recorded the occurrence of Radiolaria 

 in the Amuri limestone at Kaikoura and at the Amuri Bluff, in both of 

 which localities there are some flints in the limestone. In addition, further 

 instances of the occurrence of sponge spicules were recorded in the North 

 of Auckland in the hydraulic limestone at Kaiwaka and at Port Albert. 

 In the last locality the spicules were calcified. Also at Kaiwaka there 

 is a diatomaceous and radiolarian ooze associated with the limestone. J In 

 addition, the present paper records the presence of Globigerina ooze with 

 abundant Radiolaria and diatoms at Batley. The Globigerina limestone 



* Mr. J. H. Grenfell, of Oamaru, has kindly mounted some slides of these diatoms. 

 He says, "The following are the diatoms in these slides which appear similar to those 

 from Oamaru : Actinoptycus, Coscinodiscus, and Triceratium." 



t J. A. Thomson, The Flint-beds associated with the Amuri Limestone of Marl- 

 borough, Trans. N.Z. Inst., vol. 48, 1916, pp. 48-58 (see p. 56). 



| P. Makshall, The Younger Limestones of New Zealand, Trans. N.Z. Inst., vol. 48, 

 1916, pp. 87-99 (see p. 94). 



