Marshall. — Tertiary MoUuscan Fauna of Pakaurangi Point. 27o 



This collection from Pakaurangi Point is of rather more than usual 

 interest, as it is the first time that any attempt has been made to identify 

 or describe a Tertiary fauna of such an extensive nature from any northern 

 locality in New Zealand. 



In the first place, there are several genera that have not previously 

 been recorded from any locality in New Zealand. These are Dolicholatirus, 

 Coptochetus, Crenilabium, Spondylus, Sarepta, and the subgenus Cordieria 

 of Borsonia. On the other hand, Acteou craticulatus, Cadulus delicatulus, 

 and Crossea labiata, all members of the Recent molluscan fauna of New 

 Zealand, have not previously been found in the fossil state. The genera 

 Cymbiola and Surcula are represented by more species than is usual in New 

 Zealand fossil collections from Tertiary localities. The four species of Conus 

 that have been collected give this genus a prominence that it fails to 

 attain in any other collections from New Zealand localities. 



A more general survey shows that in this collection of 124 species there 

 are as many as forty-five, or 36-3 per cent., which have not been found 

 elsewhere, while 20-3 per cent, are Recent species. Generically and specific- 

 ally, therefore, this fauna is sufficiently distinct from any other that has 

 been recorded. There are, however, no specially archaic types, while there 

 are very many species identical with those that have been found in Tertiary 

 localities in Canterbury and North Otago in those places where full collec- 

 tions have been made. This consideration, and the further fact that nearly 

 21 per cent, of the species are of Recent occurrence, shows that the age 

 of the Pakaurangi beds is much the same as that of the beds at the North 

 Otago localities of Wharekuri and Otiake — or, in other words, of the 

 Oamaru limestone. In these localities the percentage of Recent species 

 was found by Marshall to be 23*3 and 24 respectively, but in each case only 

 some sixty species were collected. 



In my previous papers insistence has been laid on the fallacy of relying 

 too implicitly on the criterion of the percentage of the Recent species for 

 the determination of the relative age of the Tertiary strata. The personal 

 equation in connection with the identification of the species, the varying 

 depth of the water, the geographical peculiarities of the station, are all 

 matters that have to be taken into consideration before any comparison 

 of real value can be instituted. In the present case, however, Mr. Suter 

 has been good enough to examine and classify the species from both the 

 Otago localities and from Pakaurangi Point : in consequence the personal 

 equation in this comparison is of little importance. Similarly, the depth 

 of the water in which deposition of the strata took place appears to have 

 been of the same order of magnitude in both cases. Probably it was 

 off-shore water in both cases approaching a depth of 100 fathoms. 



The geographical features of the different localities may, however, have 

 an important bearing on the question. The localities are nine degrees of 

 latitude apart, and it is obvious that the species in the more northern 

 locality should suggest a warmer climate than those in a locality more 

 than six hundred miles farther south, in water relatively so shallow. 



There is also a general belief that has been expressed by various authors 

 that the climate of the New Zealand area has become relatively cooler since 

 the early and middle Tertiary times. This opinion is based on the nature 

 of the Tertiary Mollusca as compared with the Recent fauna, on the rela- 

 tively large size of many of the Tertiary species, and of the greater variety 

 of the species. Similar features have been noticed in regard to other animal 

 groups. It is, of course, obvious that a general reduction of the temperature 



