Marshall.- — Tlie Toiinr/er Limestones of New Zealand. 99 



further states that it commences at 30 fathoms and continues with some 

 frequency to 300 or 400 fathoms. At Funafuti it occurs at all depths down 

 to 200 fathoms. . 



The formation of these limestones must, therefore, have taken place 

 during a period of warm climatic conditions. Such a condition of relatively 

 warm cUmate must be regarded as exceptional in the New Zealand lati- 

 tudes, and is not likely to have been repeated within any but relatively 

 long-time periods. There is independent e\'idence that the Miocene period 

 was one of relatively warm condition-s in New Zealand, as in many other 

 regions of temperate climate. Within New Zealand such evidence is to be 

 found in the relatively large size of many species of Mollusca, of which 

 mention has be'en made by several geologists. To this may be added the 

 fact that such genera as Cijjyraea, Trigonia, and Chama then existed in 

 New Zealand, and, with Trivia, occurred as far south as Oamaru. 



That the younger limestones of New Zealand are all of the same age, 

 and represent approximately the same horizon, has already been suggested 

 by Marshall, Speight, and Cotton.* It was, however, stated in that paper 

 that the probable age of the limestone was OUgocene, this opinion being 

 based upon the classification of various groups of organisms that had been 

 collected from the limestone and submitted to experts for description. The 

 Miocene age, however, is supported not only by the nature of the molluscan 

 fossils that have been found in the limestone horizon itself at Otiake, but in 

 the molluscan fauna below the limestone at Pahi and in the TreHssick basin, 

 and in a similar fauna in the beds resting on the limestone in many locali- 

 ties. The percentage of Recent species in all of these cases amounts to 

 rather more than twenty, a fact that suggests that the age is really the 

 Upper Miocene. As has been stated on many occasions, however, it is 

 probable that too much importance has been attached to this percentage. 



The very general occurrence of Amphistegina supports the idea that 

 the limestones are of Miocene age. This genu.s, however, existed in the 

 OUgocene, though it is extremely characteristic of the Miocene. Thus 

 ChapmanI says, '' The inequilateral Amphistegina took the place of the 

 equilateral Nummulites towards the end of the OHgocene, and was the 

 predominant form in many foraminiferal deposits of Miocene age."{ 



I am greatly indebted to Mr. J. A. Bartrum, Lecturer on Geology at 

 Auckland University College, and to Mr. G. S. Thomson, of the Whangarei 

 High School, for many specimens of limestone from the North of Auck- 

 land ; to Mr. R. Speight, Curator of the Canterbury Museum, for micro 

 slices of many Canterbury limestones. I am particularly grateful to Mr. 

 F. Chapman, of the National Museum, Melbourne, for the identification of 

 the Foraminifera and for some comparative notes. 



* Marshall, Speight, and Cotton, Trans. N.Z. Inst., vol. 43. 1910, p. 407. 



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



X Since the geological range of Amphistegina is a matter of jDrime importance in 

 connection with this paper, I have made inquiries of Mr. F. Chajiman, of the National 

 Museum, Melbourne, as to the occurrence of the genus. He has kindly sent me the follow- 

 ing statement: " Amjihistegina is (leaving out doubtful forms) Cainozoic and Recent. 

 It occurs very sparingly in one or two localities in the Middle or Upper Eocene, and 

 perhaps Oligocene, in Europe ; but is increasingly abundant towards the Burdigalian 

 (Middle Miocene) ; then moderately rare till the Recent formations, when it occurs in 

 all tropical and subtropical seas. In India Amphintegina appears to be confined to the 

 Miocene. In Australia it is fairly abundant in the Oligocene, excessively abundant 

 in the Miocene, and thence to Recent more sparingly met with, when it is fomid living 

 at or near the coasts in low latitudes. Whenever it is foimd abundantly in fossil deposits 

 one may conclude we are dealing with Miocene strata." 



4* 



