332 Transactions. 



consists of very fine-grained calcite, while at Weka Pass the chambers of 

 Glohigerina, which are generally isolated, are fairly numerous. He states 

 that Radiolaria are not infrequent at Amnri Bluff, and mentions sponge- 

 spicules and several examples of a radiolarian at Kaikoura. In the highly 

 siliceous and flinty varieties at Ward and the Ure River no remains of 

 siliceous organisms could be distinguished, but he considered it probable 

 that they had been dissolved. • No explanation of the fine-grained calcite 

 base was presented, but he considered the whole rock a pelagic deposit 

 accumulated from the remains of marine organisms. 



Marshall in 1917, after the discovery of calcified sponge-spicules in the 

 hydraulic limestone of the Kaipara and Whangarei districts, re-examined 

 specimens from Ward. He considers it ])robable that diatoms and Radio- 

 laria are present, though much calcified and much destroyed by solution. 

 and sees in these the origin of the silica of the flint-beds. His argument 

 may be fairly summed up as follows : By far the greater part of the lime- 

 stone consists of very fine-grained calcite, but chambers of Glohigerina, 

 which are generally isolated, are fairly numerous. The rock is therefore 

 a Glohigerina ooze. Radiolaria are not infrequent at Amuri Bluff and 

 Kaikoura, sponge-spicules occur at Amuri Bluff, and it is probable that 

 calcified diatoms and Radiolaria are present at Ward. Therefore the 

 flint in the limestone is probably derived from the skeletons of siliceous 

 organisms. This is rendered the more probable from the occurrence of 

 diatomaceous and radiolarian ooze in limestones of similar age and character 

 in the North of x\uckland and at Oamaru. The argument would gain 

 strength by the omission of the diatomaceous earth at Oamaru, which few 

 if any other New Zealand geologists will admit to be of the same age as 

 the Amuri limestone. The facts adduced by Marshall are consistent with 

 the conclusions he derives from them, except that the fine-grained matrix 

 of the limestone is not explained ; but they are also consistent with my 

 suggestion of chemical precipitation of carbonates and silica during the 

 formation of the Amuri limestone. All that is necessary to add to my 

 account is the presence of Radiolaria and diatoms in the postulated shower 

 of Foraminifera which helped to form the limestone, the presence of some 

 siliceous sponges, and some secondary migration of the silica. 



Speight and Wild (1918) record the presence of flint both above and 

 below the phosphatic layer at Kaikoura and Amuri Bluff, and conclude 

 that its presence cannot be regarded as a criterion of age. Flint in sitv 

 just below the nodular layer occasionally shows burrows filled with glau- 

 conitic material, and so the authors remark that, unless the boring animals 

 were able to penetrate flint itself, the flint must have been precipitated 

 subsequently to the boring of the limestone. I have not claimed that 

 the presence of flint in the Amuri limestone is a criterion of age, pointing 

 out that small flints similar in mode of occurrence to those of the English 

 Chalk are common in the limestone at Amuri Bluff", which I considered 

 as much younger than the lower part of the limestone at Coverham. What 

 I did suggest was that the massive flint-beds occurring at the base of the 

 limestone from the Puhipuhi Mountains northwards occupied a definite 

 stratigraphical horizon, and Speight and Wild's observations throw no 

 light on this point. In suggesting that the silica of the flints was deposited 

 chemically I did not claim that there was no secondary migration of the 

 silica. In case I did not make this clear, I wish now to state that I 

 consider that both the flint of the flint-beds and the sporadic flints occurring 

 at higher horizons are concretionary in their nature, and are the result of 



