Marshall. — Cainozoic Fossils from Oamaru. 387 



would consider these two strata of the same age. The Oamaru limestone 

 generally consists almost entirely of remains of Echinoderms, Polyzoa, and 

 Foraminifera, though the material is generally somewhat fragmentary. 



Near the coast at Awamoa, and actually on the coast at the Eifle Butts 

 and at All Day Bay, the rocks which rest on the limestone are a bluish-grey 

 calcareous mudstone. The percentage of Recent species contained in the 

 Mollusca found in these rocks is 35, 26, and 22 respectively. The divergence 

 between these results is considerable, but the collections are of very dif- 

 ferent values. It is possible that when the collections are more complete 

 the results will be more in accord. 



The Target Gully beds are a slightly higher horizon, and the large col- 

 lection that has been made there contains 33 per cent, of Recent species. 

 The beds of Mount Harris, in rather similar material, give almost the same 

 result ; while those of Elephant Hill, which appear to be a still higher 

 horizon, contain as much as 46 per cent, of Recent species. 



Thus the relative number of Recent species gradually becomes greater 

 in the higher beds, as would, indeed, be expected ; and it is evident that this 

 result, at the least, strongly supports the conclusion as to the relative position 

 of the strata which was dependent upon purely stratigraphical observations. 



As to the actual percentages of Recent species, it is probable that con- 

 siderable changes will be made in the future as the molluscan fauna of the 

 deeper waters off the New Zealand coasts becomes better known. At the 

 present time relatively little dredging has been done, and it cannot be doubted 

 that several species hitherto believed to be extinct will be yet discovered 

 when further work of that nature has been done. It is, however, evident 

 that none of the strata from which the collections described in this paper 

 have been made is older than the Miocene period. This statement, how- 

 ever, involves the question whether any importance is to be attached to the 

 percentage of Recent species. In a country so geographically isolated as 

 New Zealand it is possible that formal change is very slow and that a 

 relatively high percentage of Recent species may be found in strata of 

 relatively high antiquity. 



Art. XLI. — The Recent Volcanic Eruptions on Ambrym Island. 



By P. Marshall, [M.A., D.Sc, F.G.S., Professor of Geology, Otago 



University. 



[Read before the Otago Institute, 1st December, 1914.] 



It is well known that geologically the New Hebrides Islands are mainly of 

 volcanic origin, and of all of them Ambrym Island is the best known because 

 of its volcanic activity. The island is near the middle of the group, in 

 latitude 16° 10' S. and longitude 168° E. It is more or less triangular in 

 shape, with its greater dimension extending for thirty miles in a direction 

 that is nearly east and west. It measures twenty-one miles in a north- 

 to-south direction. Its surface is mountainous, the highest point, Mount 

 Marum, rising to 4,380 ft., while the whole of the central portion of the 

 island rises to more than 2,000 ft. Volcanic activity was in progress on 

 the island when it was first sighted by Captain Cook, in 1774, and its 

 activity has been frequently mentioned by travellers since that date. 



13* 



