J. A. Thomson. — Age of the Waikouaiti Sandstone. 197 



Obviously, then, if Chapman's correlation of the clays of Waikouaiti with 

 the Miocene is admitted, either (a) the lower Ototaran or Waiarekan is 

 Miocene, and the opinions stated by Marshall and myself err in ascribing 

 too great an age to the Waiarekan, or (b) the Waikouaiti sandstone is not 

 Ototaran. 



During a visit to Waikouaiti at Easter, 1917, in company with Pro- 

 fessors J. Park and W. N. Benson, of Otago University, I collected from 

 the Waikouaiti sandstone at the North Head a number of brachiopods, of 

 which seventeen were referable to Pachymagas abnormis Thomson, while 

 the remaining three belonged to a small species of Pachymagas with meso- 

 thyrid foramen, probably nearly related to the more orbicular forms of 

 P. parli which occur in the Hutchinsonian of All Day Bay. 



Pachymagas abnormis was one of the species which I adduced in 1917 

 as evidence of the Upper Oamaruian age of the beds in the Takaka Valley, 

 and subsequent discoveries have not invalidated its usefulness in this 

 respect. 1 have since collected it in the uppermost bed of the Mount 

 Brown limestone at the foot of the dip slope of the cuesta opposite Weka 

 Pass — i.e., at a slightly higher horizon than the holotype, but still probably 

 Hutchinsonian — and a single specimen in the Hutchinsonian greensands of 

 All Day Bay. It occurs abundantly in the Awamoan mudstones of All 

 Day Bay, and thus ranges in the Oamaru district from Hutchinsonian to 

 Awamoan, but has not been found in the Ototaran. Now, a larger number 

 of species are known from the Ototaran of the Oamaru district than from 

 any other stage in any locality in New Zealand, so we are quite justified 

 on the present evidence in considering P. abnormis a purely Upper Oamaruian 

 species. 



Mr. S. S. Buckman, of Thame, England, has suggested in correspondence 

 that Pachymagas abnormis should not be referred to Pachymagas, but should 

 be made the type of a new genus on account of its beak characters, and if 

 this course is followed it would be possible to differentiate a number of 

 species within the somewhat variable series I have referred to P. abnormis. 

 The specimens from the Awamoan mudstones of All Day Bay and from the 

 Waikouaiti sandstone would, however, still have to be retained in the same 

 species. 



The conclusion to be drawn from the presence of this brachiopod, then, 

 is that the Waikouaiti sandstone is not Ototaran (i.e., Middle Oamaruian), 

 but Upper Oamaruian, and it may well be Awamoan, and the underlying 

 clays Hutchinsonian. In this connection an examination of the brachio- 

 pods from the sandstone at Seacliff, and from the Caversham sandstone and 

 the greensands underlying the latter rock at the back of Flagstaff, would 

 be of considerable interest, and I should be glad to receive specimens from 

 these localities. 



List of Papers cited. 



Marshall. P., 1906. The Geology of Dunedin (New Zealand), Quart. Journ. Geol. Soc, 

 vol. 62, pp. 381-424 (ref. to pp. 389-90). 



1916. The Younger Limestones of New Zealand, Trans. N.Z. Inst, vol. 48, 



pp. 87-99 (ref. to p. 93). 



1917. Fossils and Age of the Hampden (Onekakara) Beds, Trans. N.Z. Inst., 



vol. 49, pp. 463-66 (ref. to p. 465). 

 Park, J., 1904. On the Geology of North Head, Waikouaiti, and its Relation to the 

 Geological History of New Zealand, Trans. N.Z. Inst., vol. 36, pp. 418-30. 



1910. The Geology of New Zealand, Christchurch (ref. to p. 139). 



Thomson, J. A., 1917. Diastrophic and other Considerations in Classification and 

 Correlation, and the Existence of Minor Diastrophic Districts in the Notocene, 

 Trans. N.Z. Inst., vol. 49, pp. 397-413 (ref. to pp. 409-10). 



