THO-Also^■. — Geology of Middle Waipara and WeJca Pa.is Dififn'rf. 387 



earlier in this paper that the Weka Pass stone and " grey marls," as well as 

 the Mount Brown beds, are Oamaruian ; and, as Chapman refers the Weka 

 Pass stone and " grey marls " to the Eocene, it follows that the Oamaruian 

 ranges from Eocene to Miocene. The contact between the Amuri limestone 

 and Weka Pass stone is a disconformity, but bridges only the gap between 

 Danian and Eocene. 



Former geologists, notably Huttdn and Park, have correlated the Weka 

 Pass stone with the Ototara limestone, believing the lower Oamaruian beds 

 to be missing. Marshall, on the other hand, has correlated it with the 

 Hutchinsonian. The evidence of the Foraminifera suggests that it cor- 

 relates rather with the Ngaparan and Waiarekan. The evidence of the 

 molluscs is indecisive ; that of the brachiopods, on the other hand, is prac- 

 tical proof that the main Mount Brown limestone (D) is Hutchinsonian 

 and the uppermost MouJit Brown limestone (E) Awamoan, leaving all the 

 800 ft. of lower beds, down to the Weka Pass greensand, for the Ototaran 

 and Waiarekan. 



Some remarks on the relative value of the Mollusca and Brachiopoda 

 in correlation seem desirable in view of the recently expressed opinion 

 of Marshall (1919) that the latter are far less satisfactory for purposes of 

 correlation, the reasons being that they occur sporadically and in a small 

 number of species as compared with the Mollusca, and that the species are 

 hard to identify with certainty. The first is a valid objection, and is well 

 illustrated in the Mount Brown beds, which are rich in Brachiopoda and 

 yet have yielded only four specimens of Terebrahdma and none of. Lio- 

 thyrella, genera which are abundant in the Trelissick Basin and at Oamaru. 

 Nevertheless, the Brachiopoda are sufficiently widespread to enable their 

 range to be established with a considerable degree of certainty, and it is 

 illogical to neglect them if they are present in any rock and can be used. 

 The small number of species is an advantage in one respect : it enables a 

 single man to know the whole fauna intimately, and to apply to the whole 

 of it every known method of study. This- is not the case with the moUuscan 

 fauna, of six hmidred or eight hundred species ; and we can never expect 

 entirely satisfactory results until we have students confining themselves to 

 a few families, and studying these not from the point of view of New Zea- 

 land Tertiary species5 alone, but making themselves familiar with all the 

 species, both living and fossil, in all parts of the world. 



One marked difference between the Oamaruian brachiopod and mol- 

 luscan faunas is that the former is practically an extinct fauna, not sur- 

 viving the Oamaruian, except for a very small percentage, whereas the 

 latter shows a very much greater percentage of living species. The brachio- 

 pods, therefore, would be expected to be of the greater value in correlation. 



The chief disadvantages of the Tertiary moUuscan fauna are the great 

 range of the majority of the species and the different facies of the fauna 

 according to station, which makes it a matter of gTeat difficulty to ascer- 

 tain accurately the range of any given species. Until this is known it is, 

 of course, obvious that the occurrence of a species in a list gives little help. 

 Marshall (1919) has given a list of characteristic species from his different 

 series, 1)ut many of these species range widely in higher or lower series. 

 Thus, of the Nukumaru series, Suter has determined Melina zelandica from 

 the Waiarekan of the Oamaru district, and Marshall himself has recorded 

 Struthiolaria Jrazeri from the Wangaloa beds. Of the Waipipi series, Car- 

 dium spatiosum is known from the Awamoan of Oamaru and the Trelissick 

 Basin. Of the Target Gully series, Venericardia j^seutes and Terehra orycfa 

 range from Waiarekan to Awamoan, while Chama htittoni occurs in the 



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