336 Correspondotce — James Park. 



Pass Stone is conformable to the Amuri Limestone, there is a Cretaceo- 

 Tertiary formation in New Zealand, while if it is unconformable, 

 there are distinct Cretaceous and Tertiary formations. 



Mines Depabtment, J- AlLAN Thomson. 



Geological Survey Branch, 

 Wellington, N.Z. 



Ain-il 26, 1912. 



TERTIAEY FOSSILS IN THE WEKA PASS STONE, NEW ZEALAND. 



Sir, — The discovery of Tertiary fossils in the Weka Pass Stone in the Lower 

 Waipara district, as reported in this issue by Dr. J. Allan Thomson, is of special 

 interest in connexion with the Cretaceo-Tertiary controversy now taking place in 

 New Zealand. On four different occasions I had carefully searched for recog- 

 nizable fossils in this rock in the typical Weka Pass District without result, and 

 in consequence referred the Weka Pass Stone to the Cretaceous Waipara 

 succession. This discovery, it should be noted, does not in any way afiect 

 the argument for or against a Cretaceo-Tertiary succession to New Zealand. 

 What it does is to show that the unconformity between the Lower Tertiary and 

 the Cretaceous must be placed, not above the Weka Pass Stone as done by me, 

 but below it as contended by Hutton. By the aid of a sketch-map kindly made 

 for me by Dr. Thomson I had no difficulty in finding the new fossiliferous 

 locality in the Lower Waipara. Although fossils are scarce I succeeded in 

 finding two fine examples of Pseudamtismm huttoni (Park) and two of 

 Girsotrema lyrata (Zittel), both typical of the Tertiary Oamaru Series. The 

 fossils occur in the lower third of the Weka Pass Stone, and are usually not 

 many feet above the junction of the Amuri Limestone. 



Hutton always contended for an unconformity between the Weka Pass Stone 

 and Amuri Limestone. The latter is a hard grey chalky rock without bedding 

 planes. Its upper surface on which the Weka Pass Stone rests, as seen along 

 the escarpment facing Doctor's Creek in the Lower Waij)ara where the Tertiary 

 fossils were recently found, is undulating and gently corrugated, and in places 

 broken into angular fragments that have been recemented so as to present 

 a rudely brecciated appearance. But the physical break is nowhere great, and 

 since both the Weka Pass Stone and Amuri Limestone are tilted at the same 

 angle and exposed in the same scarps it is frequently difficult to distinguish any 

 trace of stratigraphical discordance. Nevertheless, the discovery of Tertiary fossils 

 in the Weka Pass Stone is a splendid justification of Hutton's contention. 

 Above Hutton's unconformity the fossils are typically Tertiary and below 

 typically Cretaceous. 



In North Canterbury the Lower Tertiary (Oamaru) Series rests on the 

 Cretaceous (Waipara) Series, but in South Canterbury and North Otago it rests 

 only on older Mesozoic or Palaeozoic rocks. Where the Oamaru Series rests on 

 these older rocks in the south it always begins with a series of terrestrial beds 

 containing seams of brown coal, but where it rests on the Cretaceous rocks in 

 the Waipara district the terrestrial beds are absent. It would thus appear that 

 marine deposition began first in the north and gradually s^Dread southward as the 

 subsidence progressed. The marine Weka Pass Stone in the north is apparently 

 contemporaneous with the terrestrial brown Coal-measures in the south. When 

 subsidence began at the close of the Cretaceous the first areas to be invaded by 

 the sea would naturally be the old Cretaceous basins, which would explain the 

 early appearance in the north of Psctidamusium huttoni and Cirsotrema lyrata, 

 both of which it should be noted pervade all the marine beds of the Oamaruian 

 in the south. 



The correlation of the Weka Pass Stone and the Ototara (Waitaki) Stone in 

 the south, as urged by McKay, is opposed to the palseontological evidence, for 

 whereas the Pareora fauna underlies the Mt. Brown (Waihao, Waitaki, 

 Duntroon, Ototara) and Kakanui calcareous horizons, it everywhere overlies the 

 Weka Pass Stone. j^^^g p^j^_ 



Otago University, Dtjnedin. 

 April 30, 1912. 



