Thomas. — Geology of Tongariro and Taicpo. 341 



before the wind, forms a long train to leeward. To the 

 north the crater-margin is partly broken down, and the sur- 

 face of the ground here is rotten and treacherous from the 

 action of the acid vapours. The hydrochloric acid in the 

 vapours reacting on the iron oxides in the scorise forms con- 

 siderable quantities of perchloride of iron, which stains the 

 ground brilliant shades of yellow and orange, distinctly 

 visible even from the top of Tongariro. 



The sides of the cone are for the most part smooth and 

 regular, and are formed of scorias and fine ashes, but here and 

 there rugged projecting rocks mark the course of lava-streams. 

 One of these, which descends as far as the south crater on 

 Tongariro, ends there in a steep front of lava, with black 

 scoriaceous surface, about 30ft. in height. This stream is said 

 to be that which flowed from the crater during the eruption 

 of Ngauruhoe in 1869. 



It has been reported that Ngauruhoe has shown great 

 signs of activity recently. I am indebted to Mr. Howard 

 Jackson, the engineer in charge of the road-makers near 

 Tongariro, for notes and sketches (see Plate XXVII.) bearing 

 on the subject. Mr. Jackson has been in the district almost 

 continuouslv for more than twelve months, within full view of 

 the mountain. He states that on the whole the mountain 

 has shown, if anything, rather less activity than usual, but 

 that during bad weather which occurred in April or May, 

 1888, a gap was formed by the breaking-in of a portion of the 

 crater- wall to the east. As seen either from the east or west, 

 there is now a deep V'^haped notch which must have the 

 depth of about 200ft. (see Plate XXVII., figs. 5 and 6). A com- 

 parison of the present outline of the cone with the drawings 

 made by Hochstetter in April, 1859 (figs. 1 and 2) shows 

 that a large amount of change has taken place since that 

 date. 



Although Ngauruhoe rises so high above the sea-level, the 

 snow does not lodge long on the cone : the ground in many 

 places is warm, and the internal heat passing slowly out- 

 wards, together with the steam rising from the crater, is 

 sufficient to thaw the snow. The steam which rises so con- 

 stantly from Ngauruhoe comes chiefly from a smaller, deeper 

 crater, with dark and steep sides, lying within the circle of the 

 principal one. From this crater ashes and fragments of 

 scorijE are frequently ejected. 



Tongariro.- — Tongariro, the third of the great mountains, 

 is, strictly speaking, composed of a number of distinct cones 

 built up around so many separate points of eruption. These 

 cones, however, are so close together that the mountain forms 

 at its base a single mass. Viewed from a distance the 

 mountain has a broad, flat-topped appearance, but as it is 



