Thomson. — Diastrophic Correlation and Districts in the Xotocene. 403 



The total thickness between the highest bed with Senonian fossils and 

 the base of the Amuri limestone is less than 150 ft. of mudstone. This 

 bed is hardly thick enough to represent the Waiarekan alone, much less 

 that stage in addition to the Wangaloa beds and any immediate beds which 

 may exist. The truth seems to be that the Wangaloa beds are represented 

 in this section by some part (probably the lower part) of the Amuri lime- 

 stone, and that the latter rock belongs to a much lower horizon than the 

 Ototara limestone. The only alternative to this view is disconformity at 

 the base of the mudstone into which the Amuri limestone passes down. 



In the districts within which they are typically developed the Amuri 

 and Ototara limestones each represent the period of maximum depression 

 or sea-advarce. These periods are, I contend, not the same, owing to the 

 masking of any general regional sea advance or advances that may have 

 occurred by the provincial warpings of distinct diastrophic districts. 



The existence of other districts of this nature is proved, as pointed out 

 above, by a consideration of the periods at which deposition commenced 

 and ceased. In further support of my thesis I now propose to give 

 palaeontological evidence which supports a difference in age between the 

 Ototara and Takaka limestones. 



In the Takaka and Aorere Valleys, including the Gouland Downs and 

 Tata Island, there is a limestone which rests almost directly on the older 

 mass of the Aorere series, being separated only by a thin bed of rolled quartz 

 pebbles, bound together in many places by a calcareous cement. The 

 limestone is followed by more or less calcareous mudstones upwards of 

 100 ft. in thickness. Higher beds are not known. From the limestone the 

 following brachiopods have been identified : Rhizothyris rhizoida (Hutton), 

 Neothyris novara (von Ihering), and a new species of Neothyris peculiar to 

 this district. From the clays in the Brown River, Aorere Valley, I collected 

 Pachymagas abnormis n. sp. (see Appendix I). The known ranges of these 

 species are as follows : Rhizothyris rhizoida occurs in all Oamaruian stages 

 from the Waiarekan to the Awamoan, but the specimens from the Wairekan 

 are dwarfed, and are perhaps to be distinguished specifically. The species 

 is found most abundantly in the Hutchinsonian. Neothyris novara occurs 

 outside Nelson Province only in the Weka Pass district, where it is confined 

 to the uppermost Mount Brown limestone, which I regard on the evidence 

 of its other brachiopod fauna and its stratigraphical relations as Awamoan. 

 Pachymagas abnormis occurs in the rmin or middle Mount Brown limestone 

 of the Weka Pass, which I regard as Hutchinsonian on the evidence of its 

 other brachiopod fauna, in the Awamoan blue clays of All Day Bay, and in 

 mudstones in the Gisborne district. 



These facts suggest that the age of the limestone is Upper Oamaruian 

 rather than Ototaran. Excluding the new species distinctive to the district, 

 all three brachiopods are known elsewhere from the Awamoan ; one is con- 

 fined, so far as present knowledge goes, to this horizon ; a second ranges 

 down only to the Hutchinsonian ; and the third, while rarely found as far 

 down as the Ototaran in its typical form, is most abundant in the Hutchin- 

 sonian. Further knowledge of the range of these species may invalidate 

 these conclusions,* and, in any case, they must be considered in connection 

 with the evidence obtainable from other groups of fossils, but until this 

 other evidence has been similarly analysed the Takaka limestone must 

 be regarded as younger than the Ototaran. In this district sea-advance 

 did not commence until after the period of maximum depression at Oamaru. 



* My statements as to the range of these brachiopods are based on the determina- 

 tion of well over ten thousand specimens from all parts of New Zealand. 



