150 Lecture on the Geology of [No. 9, new series. 



tions, tuff craters or tuff-cones. The excellence of the soil of 

 Onehunga and Otahuhu is owing to the abundance of such for- 

 mations, decomposed strata of which form the richest soil that 

 can be met with. It is curious to observe how the shrewder 

 amongst the settlers, without any geological knowledge, have 

 picked out these tuff-craters for themselves, while those with less 

 acute powers of observation have quietly sat down upon the cold 

 tertiary clays. 



After the submarine formation of the tuff-craters, the volcanic 

 action continuing, the Isthmus of Auckland was slowly raised 

 above the sea, and then the more recent eruptions took place by 

 which the cones of scoria, like Mount Eden, Mount Wellington, 

 One Tree Hill, Mount Smart, Mount Albert, and Rangitoto, were 

 formed, (*and great out-flowings of lava took place. Many pecu- 

 liar circumstances, however, prove that those mountains have not 

 been burning all simultaneously. It can easily be observed that 

 some lava streams are of an older date than others.*) In general 

 the scoria cones rise from the centre of the tuff-craters, (Three 

 Kings, Waitomokia, Pigeon Hill near Ho wick.) Occasionally, as 

 in the instance of Mount Wellington, they break through the mar- 

 gin of the tuff- crater. 



The Grater System of Mount Wellington is one of the most in- 

 teresting in this neighbourhood, as beautifully shown by the large 

 map, which Mr. Heaphy has kindly prepared for me from actual 

 survey. (*There are craters and cones of evidently different ages. 

 The result of the earliest submarine eruptions is a tuff-crater. The 

 Panmure road passes through the tuff-crater, and the cutting 

 through its brim Exhibits beautifully the characteristic outward 

 inclination of the beds of ashes, elevated from their former horizon- 

 tal levels by the eruptions, which threw up the two minor crater 

 cones south of the road — one of which is now cut into by a scoria 

 quarry. After a comparatively long period of quiescence, arose 

 from the margin of the first crater system the great scoria-cone of 

 Mount Wellington, from whose three craters large streams of ba- 

 saltic lava flowed out in a Westerly direction, extending North and 

 South along the existing valleys of the country, one stream flowing 

 into the old tuff-crater, and spreading round the bases of the small- 

 er crater cones. The larger masses of these streams flowed in 



