426 Transactions. — Geology 



marine Tertiary series is quite free from volcanic material. 

 It cannot therefore be said that the eruptions around Dun- 

 edin were a recrudescence of Oligocene activity. 



It is pretty clear that volcanic activity commenced in the 

 Dunedin area after the Caversham sandstone had been sub- 

 ject to subaerial erosion, and for that reason I am disposed 

 to place the first outbursts in the later period of the 

 Miocene, or in the beginning of the Pliocene. 



Age oj Waikoumti Leaf Beds. — I have already shown 

 that the materials composing the leaf-bed series at Mount 

 Cronin were in all probability derived from the south, prin- 

 cipally from the watershed formed by Mount Cargill range. 

 If the pile of volcanic ejectamenta forming that watershed 

 and neighbourhood was the result of Miocene eruptions, and 

 suffered subaerial erosion sufficiently prolonged to yield the 

 materials to form fluviatile or lacustrine beds at a place over 

 twenty miles distant, it is evident that the said beds cannot 

 be older than Pliocene. This conclusion is drawn from the 

 fact that the leaf beds are composed of materials derived and 

 transported by fluviatile action from a region where the parent 

 rocks rest on a higlily denuded surface of a marine formation 

 of Oligocene or Lower Miocene age. 



So far the fossil flora of these beds has not been submitted 

 to a palaeobotanist ; but, in any case, such determinations, 

 except they are supported by other data, must always l)e 

 regarded with suspicion. 



For the present, therefore, until better evidence is forth- 

 coming, I am inclined to place the leaf beds in the older Plio- 

 cene — that is, contemporary with the Wanganui older marine 

 series, and about synchronous with the lacustrine beds of 

 central Otago. 



Bearing of Waikouaiti Section on Geological History of 

 Dunedin. — From this section we learn that the piles of vol- 

 canic rocks around Dunedin were the result of at least two 

 distinct periods of volcanic activity. And the presence of 

 pumice, phonolite, and l)asanite in the leaf-bed series would 

 tend to indicate tliat the earlier eruptions were of an acidic 

 or semi-basic type. 



The materials composing the gravels of the leaf-bed series 

 were, as we have seen, apparently derived from the erosion of 

 the ejecta of the earlier eruptions, and we can only explain 

 their presence by assuming that these earlier outbursts were 

 succeeded by a period of volcanic quiescence during which the 

 newly ejected rocks were subjected to subaerial denudation. 



The basic eruptions of the second period of activity 

 smothered the newly formed gravels in the protecting cap of 

 basalt which now crowns Mount Cronin and the higher hills- 

 m the neighbourhood. 



