Marshall. — The Younger Limestones of New Zealand. 97 



In those types of limestone such as occur at Milburn, Eaglau, and 

 Cobden, where the Polyzoa are much fewer and the Foraminifera more 

 numerous and smaller, it is probable that the depth of water was much 

 more considerable — perhaps some 500 fathoms. The fossil remains found 

 in this type of limestone are relatively few, and they belong to genera 

 which may occur at considerable depths. Pecten Jmttoni, Lima laevigata, 

 Pericosmus compressus, and Magellania sp. are those that are most usually 

 found. In these rocks, again, glauconite is usually found in small quantity. 



The third type of limestone is represented by the hydrauUc limestone 

 of Auckland and the Amuri limestone of Canterbury. It is a pure Glohi- 

 gerina ooze, and may have been deposited in water of any depth between 

 600 and 2,500 fathoms, though it is not very frequent in water of a less 

 depth than 1,000 fathoms. The soundings round the New Zealand coast 

 are most numerous in the extreme north, and here it is found that such 

 an ooze covers the sea-floor at a depth of 1,095 fathoms about twenty 

 miles east of the North Cape ; generally, however, it does not occur at 

 distances less than 100 miles from the coast. Probably the hydrauhc lime- 

 stone, which contains a notable quantity of the most finely divided detrital 

 material, is analogous to the " Globigerina w. cl." <)f the charts — Globigerina 

 ooze and white clay(?) — ^which has been found at depths of 600 fathoms 

 and more near the northern part of New Zealand, and at 400 fathoms 

 seventy miles to the east of the Bay of Islands. 



The occurrence of siliceous organisms in this limestone at Amuri Blufi, 

 where the deposit is 630 ft. thick, and the highly siliceous nature of the 

 limestone near Kaikoura, Ward, and the Clarence Valley, indicate that in 

 these areas at least the water was of great depth — perhaps more than 2,500 

 fathoms — for the siliceous organic remains begin to displace the calcareous 

 types. This is the same in the North of Auckland, where much of the 

 hydraulic limestone is free from glauconitic matter, and it is often highly 

 flinty or even siliceous throughout. At Kaiwaka this Hmestone is associ- 

 ated with radiolarian and diatomaceous ooze. 



The nature of the organic remains in the limestones has not been studied 

 with any exactness, though such as the results are they certainly throw 

 some light on their age : but we still have to rely in the main on the nature 

 of the organisms contained in the strata associated with the limestones. 

 It is a matter of very general agreement that the limestones at Te Kuiti, 

 Raglan, Wiwiku Island, Mokau, Tata Islands, Mount Soniers, Oamaru, Mil- 

 burn, and Winton are of Miocene age. In nearly all of these locaUties these 

 limestones are associated with strata that contain a variety of Miocene 

 fossils. These fossils are mainly moUuscan, and they have been regarded 

 as Miocene chiefly because of the high percentage of Recent species that 

 are represented — 20 per cent, or more. 



The Whangarei limestone is not so easily dismissed. No moUuscan 

 fossils have yet been recorded in strata that are associated with it, and 

 it becomes necessary to consider again the nature of the organisms that 

 occur in it. The presence of Amphistegina is of great importance in this 

 connection. This genus appears to be regarded as a typical Miocene 

 genus. Thus Chapman says, "The inequilateral Amphistegina took the 

 place of the equilateral Nummtdites towards the close of the OHgocene, 

 and was the predominant form in many foraminiferal deposits of Miocene 

 age."* The frequent occurrence of Amphistegina in the Whangarei lime- 

 stone thus points decisively to a Miocene age for this rock, and this 



* F. Chapman, Mem. Nat. Mus. Melbourne, No. 5, 1914, p. 23. 

 4 — ^Trans. 



