12G Transactions. 



of early or Middle Tertiary alge. There is certainly a striking poverty of 

 moUusca in the Wanganui beds when they are compared with that of the 

 very small exposure of fossiliferous strata at Target Gully, near Oamaru, and 

 elsewhere in the Middle Tertiary strata. This relative poverty in species is 

 certainly not due to less careful collecting at Wanganui, for a greater amount 

 of time has been spent in the latter locahty and a much greater variety 

 of strata has been scrutinized than at Oamaru. There are no additional 

 genera of any importance in the Castleclifi strata, and there is no sudden 

 inrush of new species, so far as our investigations go, at any horizon of 

 the beds exposed on the coast-line between Wangatiui and Waipipi. 



(3.) A considerable and general change of climate must naturally have 

 a great effect upon the molluscan life on the coast-line. It is, of course, 

 well established that towards the close of Tertiary time in Europe and in 

 America and elsewhere there was a great change in climate, especially 

 during the Pliocene period. The high percentage of Recent species of 

 mollusca in all the strata with which this paper deals shows clearly enough 

 that they are of Upper Tertiary age. Those at Waipipi perhaps correspond 

 to the early Pliocene of Europe, or perhaps to the later Miocene, while the 

 CastleclifE beds probably represent the highest Pliocene. The change in 

 molluscan fauna may therefore be mainly due to the gradual reduction 

 ■ of temperature that was a feature of all climates during the Pliocene 

 period. The faunal change in this district seems to have been much less 

 rapid in the upper portion of the strata examined than in the lower ones. 

 In the 960 ft. of strata between Castleclifi and Kai Iwi only 2-5 per cent, 

 of extinct species appear, while in the 1,050 ft. between Kai Iwi and 

 Nukumaru an additional 14 per cent, appear, and between Nukumaru 

 and Waipipi, in a thickness of 1,450 ft. of sediment, 15 per cent, more of 

 extinct species are found. In other words, between Waipipi and Nuku- 

 ^maru 1 per cent, of the species becomes extinct in every 97 ft. of sediment. 

 Between Nukumaru and Kai Iwi the rate is 1 per cent, of extinction for 

 every 75 ft. of sediment, and between Kai Iwi and Castleclifi" the rate is 

 much slower and amounts to no more than 1 per cent, in a thickness of 

 384 ft. of sediment. The general average of extinction for a total thickness 

 of 3,560 ft. is almost exactly 1 per cent, of the species in every 100 ft. 

 If, as suggested before, this sediment has been deposited at an average rate 

 of 1 ft. in 200 years, it follows that on the average during the greater part 

 of the Pliocene period in New Zealand 1 per cent of the species of marine 

 mollusca has become extinct in every 20,000 years. It is not intended 

 to assert any accuracy for this result, though it is thought that it is of the 

 same order of magnitude as the actual result would be if all the various 

 factors could be ascertained with certainty. 



It has been stated earlier that, as far as the stratigraphy can be seen in 

 the marine clifi's, there is certainly no sign of any unconformity. The 

 clifis give an actually continuous section from Castleclifi to Nukumaru. To 

 the north of Nukumaru the continuity is interrupted for a considerable 

 distance, but the close' resemblance of the fauna of the Waipipi beds to 

 that of Nukumaru in itself points to the conclusion that deposition was 

 continuous. This idea is strongly supported by the fauna which is found 

 at Wilkie's Bluft", on the left bank of the Waitotara River, two miles 

 and a half below the railway-bridge, a locality intermediate between 

 Nukumaru and Waipipi. Here there is a great abundance of Ostrea 

 ingens, with Pecten triphooki and some Cardium spatiosum and Ltitraria 

 solida. Palaeontologically as well as in geographical position the bluff 



