238 Transactions. 



movements instead of overlap. Of this there is at present no proof what- 

 ever. Certainly the continuity of the Tertiary strata between the Waihao 

 and Shag Point gives no suggestion of such a series of movements as 

 would be required to account for the different age of the lowest strata 

 of the series of younger rocks (Oamaru system) in different parts of that 

 district. 



A further comparison of the Hampden fauna with that of other horizons 

 in the Oamaru district is also of interest. This comparison should begin 

 with those strata that are oldest. In my opinion the oldest from which 

 collection has been made (with the exception of the Hampden and of 

 the Shag Point beds) is the Bortonian of Park. That is also the opinion 

 of Park, who says, "' The Bortonian is the lowest marine fauna of the 

 Oamaruian in North Otago, if not in New Zealand."* The list of Mollusca, 

 however, which he gives is relatively small, for it contains onlv forty-three 

 species. In another respect also it is rather strikingly different from all 

 the other collections that have been made in North Otago, as it contains 

 twenty species — nearly half of the total — of lamellibranchs. This may 

 be due to a shaUower-water station or to the imperfect preservation of the 

 smaller species of gasteropods. 



The beds from which this collection was made are composed of a quartz 

 sandstone which must have been deposited under conditions quite different 

 from those under which the Hampden beds were deposited. Under these 

 circumstances it would not be expected that the faunas from these two 

 localities would show very great resemblance even if they were of the same 

 age. In actual fact but little resemblance can be discovered. It is, how- 

 ever, noticeable that Sinwn elegans Suter and Surcula serotina Suter occur 

 in both formations, and that these species have been found in the lower 

 formations of the Oamaru district only. 



The horizon that appears to me to be next in the order of age in the 

 Oamaru district is that of the greensand of Waihao. Collections from this 

 horizon were listed in 1914, t but the collections were very small. Out of 

 thirty-three species some 12 per cent, were found to be Recent. Six of 

 these species, however, have been found in the Hampden and Waihao beds 

 only up to the present time. These are — Ampullina waihaoensis Suter, 

 Exilia waihaoensis Suter, Turris duplex Suter, Turris regius Suter, Turris 

 complicatus Suter, and Surctda serotioia Suter. The last of these has been 

 found in the Bortonian also. 



The occurrence of these species in the two beds is of special importance 

 when it is realized that all of them are absent from the Awamoa and Target 

 Gully localities, in which large collections have been made, numbering 87 

 and 212 species respectively. These two localities topograjihically lie 

 directly between the Hampden and Waihao greensand deposits. The 

 Waihao greensands lie stratigraphically between the quartz sands with 

 coal — probably the Bortonian beds of Park — and the Oamaru or Ototara 

 limestone horizon. Another stratum which occupies the same local strati- 

 graphical position and has the same lithological nature is the Wharekuri 

 bed ; but this lies farther to the west, and on the assumption of the correct- 

 ness of the theory of continuous overlap the Wharekuri beds, which lie 

 farther to the west, would be of greater age than the Waihao greensands, 

 which are situated twenty miles farther to the east and in a region, therefore, 



* J. Park, X.Z. Geol. Surv. Bull. No. 20, p. 34, 1918. 

 t P. Marshall, Trana. N.Z. Inst., vol. 47, p. 385, 1915. 



