Pakk. — On the Geology of North Head, Waikouaiti. 429' 



Manii Hill is an ideal site for the University astronomical 

 observatory. 



Diiratiou of Volcanic Cessation. — The means to determine 

 this are only comparative. The leaf beds at Waikouaiti and 

 Kaikorai and the shale-beds ac Waitati rest directly on the 

 Caversham sandstone, from which we gather that the earlier 

 eruptions did not reach these areas. 



On the other hand, the fine silts, muds, and ash at these 

 places clearly indicate that showers of finer ejecta at times 

 fell in the lake- basin in which these deposits were forming, 

 and doubtless also on the surrounding country. The gravel- 

 beds which close the leaf-bed series, moreover, prove that 

 iluviatile forces were active agents of ei'osion immediately 

 prior to the beginning of the second and final era of volcanic 

 activity, which culminated in the emission of the lavas over- 

 lying the gravels. 



The plant-remains in the muds and silts inform us that a 

 varied forest vegetation grew on the shores of the Pliocene 

 lake ; while the oil-shale at Waitati may be held to indicate 

 the existence of a rich and long-continued growth of fresh- 

 water gelatinous algae or related forms. 



At Te Manu Hill, near the Mining School, the silt and 

 gravel series rests on a surface of coarse volcanic breccia, a 

 circumstance which clearly indicates that the eastern shores 

 of the Pliocene lake reached to the area affected by the earlier 

 volcanic eruptions. 



The gravels and tuffs which close the leaf-bed series seem 

 to have suffered little or no erosion prior to the renewal of 

 volcanic activity. They were apparently overwhelmed sud- 

 denly by stupendous outbursts, more violent and widespread 

 than those of the earlier period of eruption. We may there- 

 fore conclude that the period of cessation was approximately 

 equivalent to the time required for the deposition of the inter- 

 calate leaf-bed series. 



After the period of cessation volcanic activity commenced 

 anew, culminating in the more basic outbursts in newer 

 Pliocene times. 



Direction of Drainage in Pliocene Times. — A study of the 

 section at Mount Cronin affords some interesting information 

 respecting the conformation of the land during the interval of 

 volcanic cessation. 



Professor Ulrich showed that the volcanic rocks around 

 Dunedin graduated from trachytoid phonolites to basanite.''' 

 The preponderance of phonolite and basanite in the Mount 

 Cronin gravels is therefore highly instructive. It shows, in 



* Trans. Aust. Assoc. Adv. Science, vol. iii., 1891, p. 145. 



