Marshall. — Fauna of tht Hampden Beds. 237 



Cossmann to be possibly identical with G. paucisulcata Marshall from 

 Wanaaloa. In addition the followina,' sjx'cies occur in both of these beds : 

 Cucullaea alia Sow., TurriteUa symmetrica Hutton, Bullitiella e)i//si Hutton, 

 Dentalium mantelli Zitt., Struthiolaria minor Marshall. 



I have previously stated that in my opinion the Wangaloa beds are 

 the oldest Tertiary horizon that has yet been recognized in this country, 

 and that the occurrence of Perissolax and PugneUus shows that there were 

 some Cretaceous MoUusca still in existence. In addition Gilbertia and 

 Heteroterma suggest an extremely early Eocene or perhaps a Paleocene 

 age as an equivalent. The further fact that the percentage of the Recent 

 species sinks as low as 8 again supports the view as to the antiquity of 

 these beds. This opinion as to their great antiquity is supported by 

 Trechmann* and by Thomson. f The percentage of Recent species in the 

 Hampden beds is about the same as in the collection from Wangaloa, but 

 the Recent species are not the same in the two localities. 



In addition the antiquity of the Hampden beds is shown by the presence 

 of the genera Gilbertia, Volutoderma, Trigonia, and Dicroloma. These 

 genera, however, with the exception of Gilbertia, are not the same as those 

 of high antiquity in the Wangaloa collection. This difference in details 

 may, however, be due to the different lithological nature of the strata, and 

 therefore, in all probability, of the station at w^hich deposition of the strata 

 took place. The Wangaloa beds are quartz sands with a small amount 

 of glauconite. The Hampden beds, on the other hand, are formed of an 

 extremely unctuous mud, in which, however, there is a large amount of 

 glauconite. 



I believe that in the present state of our knowledge of the range of 

 genera and species in the older Tertiary rocks both in space and in time 

 it is unreasonable to insist on the occurrence of considerable numbers of 

 identical genera and species of fossils for the correlation of horizons, for 

 we cannot at present make proper allowance for the differences that are 

 due to station. On the other hand, the outcrops of these older Tertiary 

 rocks are so isolated from one another that in view of the generally 

 accepted belief in the great overlap in their stratigraphical relations it is 

 very undesirable — if, indeed, possible — to classify all the Tertiary rocks 

 on a basis of purely stratigraphical considerations, as has lately been 

 attempted by Thomson. 



For these reasons it is in the opinion of the author far better to base 

 the classification of these rocks on the general affinities of the fossil fauna 

 contained in them. This may be most conveniently effected by comparing 

 the faunas in such a way as to show the percentage of species that are 

 common to the various strata, and in particular by paying special attention 

 to the percentage of Recent species that occur in the various collections 

 that have been made. The Recent fauna is particularly suitable for this 

 comparison, since it contains species that have littoral occurrence as well 

 as those which occur in water of moderate depth. This comparison may, 

 however, tend to suggest rather too great an age for those strata which 

 were deposited in deep water, because the molluscan fauna of our deep- 

 water areas is still most imperfectly known. 



Thomson, indeed, now suggests that the geographical separation of 

 the outcrops of our Tertiary formations is due to minor diastrophic 



* C. T. Trechmann, Geol. Mag., dec. 6, vol. 4, p. 296, 191' 

 t J. A. Thomson, Tra7is. N.Z. Inst., vol. 49. p. 402, 1917. 



