342 Traitsactions. — Geohgy. 



Art. XLIV. — Observations on the Eruption of Mount Tarawera, 

 Bay of l^lenty, New Zealand, IQth June, 1886. 



By J. A. Pond and S. Percy Smith, F.R.G.S. 



[Read before the Auckland Institute, 12th July, 1886.] 



The 10th of June, 1886, is likely ever to be remembered in the 

 history of New Zealand as that on which the colonists first had 

 practically brought home to them the fact that the volcanic 

 forces for which these islands are so celebrated had still 

 an amount of vitality in them that was unlooked for and 

 unexpected. The eruption of Tarawera Mountain, and the con- 

 version of Eotomahana Lake into a crater, on that date, at 

 about 2.15 a.m. has caused widespread consternation, the loss of 

 several lives, and a feeling of anxiety as to whether this out- 

 burst will be confined to the immediate district where it occurred, 

 or whether it will spread to others in which the signs of thermal 

 action have been known for long periods. 



Description of Volcanic District. 



The volcanic districts of the North Island have been correctly 

 described by Hochstetter as occupying three zones : the first, as 

 that from Tongariro to White Island ; the second, as that of the 

 Isthmus of Auckland ; the third, as that of the Bay of Islands. 



There are many very essential differences in the general 

 character of the results of volcanic action in these three zones, 

 the first-named being that in which any extent of vitality 

 appears to have remained unto the present day ; though the 

 Bay of Islands District has still its group of hot springs, whilst 

 that of Auckland, so intimately known to all of us, has ceased 

 to show any sign of life at all, though exhibiting to the observer 

 some of the most perfect examples of extinct volcanic action 

 in its several stages known to the world. Of these essential 

 differences, the most prominent, and those which alone require 

 notice on the present occasion, are the characters of the rock- 

 masses and materials which go to build up the vast accumula- 

 tion of volcanic remains forming the mountains and ejected 

 matter in the different districts. The rocks of the central or 

 Taupo zone are composed of materials known generally under 

 the name of "acidic" rocks, whilst those of the other two zones 

 are — in their latest manifestation, at all events — entirely formed 

 of basic rocks. We may take, as general names descriptive of 

 these two classes, trachytic rocks for the acidic areas, basaltic 

 rocks for those of the basic areas, the distinction being in the 

 nature of the constituents and their forms of aggregation. 



The researches of modern science tend to confirm the idea 

 that there is a regular sequence in the order in which these two 



