Shkewsbuky. — On the Auchlayid Volcanoes. 379 



which passes through the New Hebrides and New Guinea, 

 and then forks, one branch being continued northwards 

 through the Pliilippine, Japan, and Kurile Islands to Kam- 

 tchatka, the other westward, through Java and Sumatra. 

 New Zeahxnd therefore represents a continuation in a south- 

 westerly direction of this volcanic belt, and the elevation of 

 the North Island was probably due to volcanic activity. It is 

 now well known that in the majority of cases volcanic erup- 

 tions commence with the formation of a fissure or fissures in 

 the earth's crust. It is probable, therefore, that previous to 

 the outburst of volcanic activity''' in what is now the isthmus 

 of Auckland disturbances took place in the direction of the 

 line above stated, and a deep fissure was formed running in 

 that direction, from which numerous minor fissures branched 

 off at right-angles. 



As regards the conditions attending the earliest eruptions 

 and the surface-features at the time, we have seen above that 

 most of the tuff-craters were formed under the sea. On this 

 point Hochstetter says, " The first outbursts, as a closer 

 examination shows, w^ere probably submarine ; they took place 

 at the bottom of a shallow muddy bay, little exposed to waves 

 and wind." He fails to notice, however, that, though the 

 earliest eruptions were submarine, dry land had previously 

 existed — that, in fact, the land was submerged only just pre- 

 viously to the commencement of volcanic activity. That this 

 is so is shown by the presence at the Panmure basin of a bed 

 of vegetable matter (in composition intermediate between peat 

 and lignite) immediately underlying the volcanic tuff. Logs, 

 stumps, flax, &c., have also been found under the tuff at 

 other points on the isthmus. The bed at Panmure is several 

 feet in thickness, and contains stems and branches of trees, 

 some of them of considerable size. This points to a luxuriant 

 vegetation covering the ground at the time the first eruptions 

 took place, and proves that dry land must have been in existence 

 for a long period before the submergence took place and volcanic 

 action began. The sequence of events therefore seems to have 

 been this : After their original upheaval the Waitemata beds 

 suffered the usual weathering and denudation, and became 

 covered — at least in places — with vegetation ; subsequently, 

 just previous to and probably as a result of the same earth-move- 

 ments as produced the eruptions, a depression took place, until 

 parts of the isthmus were submerged beneath the sea. A 

 fissure was then formed, and volcanoes burst out under the sea 

 in various places, forming the tuff-craters. Then, as stated by 



* This period of volcanic activity must not be confused with the 

 antecedent period of activity during which the Manukau and Cape 

 Colville breccias were formed, and the distribution and contour of the 

 land were very different from the features now existing. 



