430 Transactions. — Geology. 



the first place, the southern origin of the leaf-bed material ; 

 and, as this material is obviously water-borne, it establishes 

 the former existence of a drainage system running from south 

 to north — that is, from Dunedin towards Waikouaiti, in a 

 direction more or less parallel with the general trend of the 

 present coast-line. 



Again, the physical conditions and distribution of the ma- 

 terials in the different members of the leaf-bed series tend 

 to show that this drainage system comprised a river with one 

 or more shallow lakes along its course. 



This ancient watershed required for its outer or eastern 

 rim the existence of a land-area to seaward of the present 

 coast-line, and it just suggests itself that this rim was pro- 

 bably formed of volcanic ejecta piled up during the earlier 

 period of eruption. At any rate, there is evidence that the 

 earlier eruptions did not extend so far south, west, or north 

 as the later outbursts, but were centred in the neighbourhood 

 of Port Chalmers, Purakanui, and Mount Cargill. 



The geological history of volcanic activity around Dunedin 

 in Tertiary times bears a peculiar likeness to that of the 

 Hauraki goldtields of Auckland. After a study of tlie latter 

 extending over seven years, I wrote in 1897 as follows : 

 " After the pent-up forces had spent themselves in the first 

 great paroxysm there was a period of rest, during vvhich 

 vegetation established itself on the muds and ashes washed 

 into the low ground by the streams draining the slopes of the 

 newly formed volcanoes. The land, however, was in a con- 

 tinued state of tremor, and the oscillations were too frequent 

 to permit the continued growth and accumulation of sufficient 

 vegetation to form workable seams of coal. The cessation of 

 volcanic activity was of short duration. The plutonic forces 

 burst out with renewed energy. The forests were devastated 

 and utterly destroyed, and covered with hundreds of feet of 

 ashes and solid lava of semi-basic character."* 



DESCRIPTION OF PLATE XXXII. 

 Section, Waikouaiti North Hkad. 



1. Talus deposit. 



2. Basalt-flow. 



.3. Gravels and sands. 



4. Grey sandstone. 



5. Calcareous sandstone. 



6. Blue clays, foraminiferous. 



Section of Summit of Mount Cronin. 



2. Basalt-flow. 



.3a. Grey sands and silts. 



36. Coarse grits. 



3c. Grey silts and sands. 



3<i. Coarse gravels. 

 8/. Sandy grits. 

 4. Grey sandstone. 



• Park, " The Geology of the Hauraki Goldtields," 1897, p. 43. 



