242 Transactions. 



50 ])er cent. — into the divisions above and below. It is therefore necessary 

 to exercise the greatest care in selecting those species which are to be 

 regarded as the distinctive species of any one horizon. Even yet our 

 knowledge is probably not quite sufficient to allow us to do so in all 

 cases with great confidence. But even where this is so it does not justify 

 us in neglecting the large amount of palaeontological knowledge we now 

 have, as is actually done by Thomson. 



As stated before, endless confusion would be caused by attempts to place 

 the various beds near Oamaru in the stages as defined by Thomson. What, 

 for instance, is the position of the Wharekuri beds ? There is no Ototara 

 limestone near them, and there is no Waiareka tuff, and there are no beds 

 that in any way resemble the blue clays of the Awamoa stage. In our 

 old classification of 1911 they had already a definite place, though it was 

 regarded as provisional only. Park without any hesitation classes them 

 in the Hutchinsonian because, he says, they lie below his Waitaki stone 

 and above his lignitic beds.* This is at best a guess, and Thomson, with 

 all oth^r geologists except Park, refuses to recognize any difference between 

 the Ototara and Waitaki limestones. Palaeontological results, however, 

 can here be utilized with advantage, for seventy-five species of Mollusca 

 have been found in the Wharekuri beds. If the general relationship of this 

 fauna and the percentage of Recent species can be taken as a guide it can 

 be clearly shown that the horizon is lower than that of the Ototara lime- 

 stone and higher than the Bortonian of Park. 



The reason for all of this is that Thomson maintains that the fauna of 

 each localitv is still imperfectly known, and he will not accept any fauna 

 as characteristic until repeated visits to a locality fail to result in the col- 

 lection of additional species. He states that he has examined ten thousand 

 specimens of brachiopods from all parts of New Zealand, and says that 

 until a similar investigation has been made of the Mollusca no rock grouping 

 can rightlv be based upon them. Actually I have examined far more than 

 ten thousand specimens of Mollusca at Target Gully alone, and many times 

 this number of specimens in other parts of New Zealand. More than eiglit 

 hundred species of Tertiary Mollusca that occur in New Zealand have now 

 been described, and the number of species recorded from several localities 

 is now more than sixty. vSurely our knowledge is now sufficient to allow 

 us to adopt a palaeontological basis for our grouping of the rocks of the 

 Oamaru system. 



The basis of classification that has been found satisfactory in all parts 

 of the world is dependent upon the occurrence of genera or species which 

 have a restricted range in time. Unless a clear secpience of fossiliferous 

 strata is found in any locality, or unless some rough grouping of the rocks 

 is first obtained, the range of species is in general rather hard to determine. 

 There will, however, always be some species that have a restricted range 

 in anv one fossiliferous locality, and by comparing those species that have 

 a short life in different localities a classification can soon be arranged. 



Attenipts which have been made to do this in New Zealand have not u}) 

 to the present time proved very successful. The more accurate identifica- 

 tion of fossils and the more extensive collecting of recent years have, 

 however, now made it possible. Some of our genera in particular are 

 specially suited for this. Struthiolaria appears to me to be one of the best. 



* J. Park, Bull. N.Z. Geol. Surv. No. 20, p. 84, 1918. 



