98 Transactions. 



organism may be used to correlate all those limestones in which it occurs, 

 for it appears to be the same species in all of them. The stones from the 

 following locaUties contain this species : Wiwiku Island, Kawhia, Tata 

 Islands, Culverden, Otaio, Mount Somers, Oamaru, and Winton. 



It appears to be the general opinion of geologists that the Whangarei 

 limestone is a lower horizon than the hydraulic limestone in the North of 

 Auckland, or at least that the two limestones belong to the same series. 

 If this is the case, the hydraulic limestone also cannot be older than 

 the Miocene. The suggestion is in part supported by the occurrence of 

 Cucullaea and Dentalium in this rock at Limestone Island, Whangarei 

 Harbour, specimens of which were on view in the Auckland Exhibition of 

 1913. It is further supported by the occurrence of a varied Miocene 

 molluscan fauna in the greensands below the hydraulic limestone at Pahi.* 



The Amuri limestone still remains to be considered. It has already 

 been stated that microscopic examination of the Amuri limestone at Weka 

 Pass, and of the Weka Pass stone which rests on it, has shown that the 

 limestones have an identical composition in kind both mineralogically and 

 organically, and that the differences between these two strata, so far as 

 specimens taken from the immediate neighbourhood of the junction are 

 concerned, are due solely to the difference of proportions of the various 

 constituents. Very few molluscan fossils have as yet been obtained from 

 the Amuri stone. Pecten zitteli Hutton is practically the only species. In 

 the Trehssick basin, however, Thomson and Speight have discovered a 

 molluscan fauna in the beds beneath the Amuri limestone, and at the Weka 

 Pass the Weka Pass stone, which rests on the Amuri limestone, also con- 

 tains a Miocene fauna. Again, the Otaio limestone, which is always regarded 

 as an outcrop of the Amuri limestone, and which is a very fine-grained type 

 of rock with an abundance of Glohigerina, also contains this Amphistegina, 

 which is apparently the same species as in other parts of the country. 



This Amuri limestone has always been correlated with the hydraulic 

 limestone of North Auckland. It is quite reasonable to suppose that these 

 two rocks are of the same age. Under the microscope the two cannot be 

 distinguished, and their composition indicates that they were deposited on 

 an oceanic floor in deep water. This implies great depression, which is 

 likely to have taken place during the same earth-movements in locahties 

 that are relatively close to one another. If this correlation, which has been 

 so very generally adopted, is correct, the Amuri limestone, like the Wha- 

 ngarei limestone and the hydraulic limestone, must be of approximately 

 the same age as the Oamaru and other limestones that are so largely com- 

 posed of remains of Foraminifera. 



The presence of Amphistegina in so many of these limestones both north 

 and south supports the correlation of the limestones from another and quite 

 a different point of view. So far as our knowledge of the New Zealand 

 Foraminifera goes at present, the genus Amphistegina does not occur in our 

 waters. There is no mention of it in Hutton's " Index Faunae Novae 

 Zelandiae," nor in Haeusler's accomit of the Foraminifera in the Hauraki 

 Gulf, nor in Chapman's description of the Foraminifera dredged in 110 

 fathoms west of the Great Barrier. The genus is, however, well repre- 

 sented at the present day in the warmer waters of the Pacific Ocean. Thus 

 Bradyt states, " In the living condition Amphistegina is distinctly a tropical 

 genus ; its home is among the shallow-water sands of warm seas." He 



* J. Park, N.Z. Geol Surv., 1885, p. 168. 



t ** Foraminifera," Chall. Rep., vol. 9, p. 741. 



