Marshall. — The Hampden Beds and N .Z. Tertiary Limestones. 113 



more deeply depressed during this middle Tertiary period tlian Otago, a 

 fact that is clearly evidenced by the very nature of the Amuri limestone, 

 which is often wholly composed of Globigerina, but in some cases of other 

 pelagic organisms as well. In Otago, on the other hand, the limestones, 

 whilst still free from all terrestrial sediment, consist mainly of organisms 

 that live on the floor of moderately deep water only. While this is the 

 case, however, it must still be remembered that at Oamaru the limestone 

 rests on a deposit that is composed of diatoms, Radiolaria, and sponge- 

 spicules. Park (1918, p. 50) has lately maintained that this is really a 

 slaallow-water deposit, an opinion that is based partly on the general 

 geology of the district and partly on the nature of the moUusca and 

 brachiopods that are found in the deposit. The fossil species to which he 

 refers are not named. In a collection made by me in June, 1915, the 

 following mollusca were obtained : Amusium zitteli (Hutton), Nuculana 

 [Leda) sp., Lima sp. (small), and Terebratulina suessi (Zittel). These are 

 all genera that have a wide occurrence in deep water, and until a list is 

 published which contains the names of other molhisca that have a shallow- 

 water habitat there is no reason to suppose that the moUuscan remains 

 in these diatomaceous deposits are incompatible with the accumulation 

 of the material on a deep oceanic floor. There is no reason to suppose 

 that the water was of the same depth over all that portion of New Zealand 

 that was then covered by the ocean. In Canterbury the area in which 

 the Amuri limestone occurs was covered by deeper water than that portion 

 of Otago where the Oamaru or Ototara limestone is found. It may there- 

 fore fairly be said that all the palaeontological evidence that is known at 

 the present time supports the belief that the Oamaru limestone represents 

 an horizon of the Amuri limestone, and that there are no stratigraphical 

 or structural facts known that oppose this conclusion. 



In the north of Auckland the so-called hydraulic limestone covers a large 

 area. This limestone is also composed mainly of Globigerina ooze, and, 

 like the Anuiri limestone, it is often highly siliceous, and in places the siliceous 

 organisms are calcified, though at others diatoms, Radiolaria, and sponge- 

 spicules are in a perfectly fresh condition and can be obtained in large 

 numbers. This limestone has generally been correlated with the Amuri 

 limestone of Canterbury, and Thomson's objection to this has already been 

 refuted (Marshall, 1919, p. 248, footnote). In addition, however, to the 

 general stratigraphical position of this limestone, there is palaeontological 

 evidence of considerable importance. At Pahi, on the Arapaoa arm of the 

 Kaipara Harbour, there is on the foreshore a little to the west of Pahi 

 Township a bed of greensand lying between two beds of the hydraulic 

 limestone. This greensand contains a considerable number of fossils, as first 

 noted by Park. The fossils, however, are in a bad state of preservation, 

 and only a few of them can be identified specifically. The following were 

 collected in 1916 : — 



yAtrina sp. 



Calliostoma sp. 



Cassidea n. sp. 



Corbida canaliculata (Hutt.) 



Cucullaea alia (Sow.) 



Cythere'a sp. 



Deiitalium solidum (Hutt.) 



Divaricella afi. cumingi (Ad. & Ang.) 



Limopsis zitteli (Iher.) 



Nucula sp. 



Nuculana aff. hellula (A. Ad.) 



Ostrea aff. corrugata (Hutt.) 



Panope worthingtoni (Hutt.) 



Polinices gihhosus (Hutt.) 



Psammobia sp. 



Struthiolaria sp. 



Stircula n. sp. 



Tellina sp. 



Turritella ambidacrum (Sow.) 



Venericardia aff. australis (Lamk.) 



