538 Transactions. — Geology. 



6. Dentalium majus, Hutton. 



7. Zenacia acmaces, Quoy and Gaimard. 



8. Ghione vellicata, Sowerby. 



9. Ghione stutchburyi, Gray. 



10. Meretrix assimilis, Hutton. 



11. Dosinia australis, Gray. 



12. Venericardia australis, Lamarck. 



13. Glycimeris globosa, Hutton. 



14. Pecten radiatus, Hutton. 



15. Ostrea angasi, Sowerby. 



16. Anomia alectus, Gray. 



17. Psammobia lineolata, Gray. 



18. Mactra aqu'Uatera, Deshayes. 



19. Tapes intermedia, Quoy and Gaimard. 



Of the eighteen molluscs in this list, thirteen, or 61 per 

 cent., are still living, a percentage which clearly places these 

 and the associated beds in the Pliocene. 



The Motanau beds, although correlated by the Geological 

 Survey with the Pareora series, contain none of the shells 

 characteristic of the Pareora fauna. As will be shown pre- 

 sently, the Pareora fauna occurs in the underlying Mount 

 Brown or Mount Donald beds. 



The Motanau beds rest upon a denuded surface of the 

 underlying Mount Brown beds. The unconformity between 

 the two series was recognised by Sir James Hector* in 1868, 

 and by Sir Julius von Haastf in 1870. Both writers referred 

 these beds to the Pliocene. The former noted that the beds 

 contained " many specimens of marine shells that are still 

 alive," and had been deposited " in basins excavated in the 

 older Tertiary rocks" — that is, in the Mount Brown beds. 

 After an interval of thirty-four years I am compelled to once 

 more refer the Motanau beds back to the Pliocene. 



Mount Broicn Beds. 



At 43 miles 3 chains from Christchurch the railway-line 

 enters a cutting which is a little over 6 chains long. The 

 bank on the west or Weka Stream side of the line rises from 

 a few feet high at the lower end to 26 ft. high near the north 

 end, whence it drops to nothing somewhat more abruptly. 

 The section exposed in this cutting is of great importance, as 

 here the Motanau beds are seen to rest unconfonnably upon 

 the Mount Brown beds. The Motanau beds lie on a denuded 

 surface of the Mount Brown beds, and the section is so clear 

 that no doubt can be entertained as to the unconformable 



* Hector, Progress Report, p. xii., Reports of Geol. Survey, 18G8-69. 

 I Haast, Reports of Geol. Kxpls., 1870-71, p. 15. 



