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



knew not to what brimstone depths an unwary step might sink us. 

 Our difficulty in walking, therefore, arose less from the heat, 

 though that in places was great, than from the apprehension of 

 sinking too far in the soft crustaceous surface, from which diminu- 

 tive spouts of vapour would spit forth as if to resent our intrusion. 

 Whenever we thought the ground at all doubtful, we sounded our 

 way by hurling large stones to see what impression they would 

 make, and we adventured or avoided proceeding accordingly. 



Time, to our great regret, would not admit of a minute explora- 

 tion, but all the grand features of the island had passed under 

 view. We looked in vain for the gorgeous meadow described by 

 Captain Drury ; but we had only to enlarge any of the numberless 

 miniature vapour holes to obtain pure crystallised sulphur hot from 

 the bakery, and at the same time to convert these holes into more 

 active vapour jets. The streams that issued in various directions 

 were of boiling heat, limped and tasteless ; but though sulphur 

 was everywhere strewn around, it did not appear to be in quantities 

 sufficient for shipment. After an hour's stop, we returned to our 

 ship greatly delighted with the visit, and much indebted to our 

 obliging Captain for having put it in our power to enjoy it. 



Mr. Heaphy has kindly furnished me with a map and views of 

 this singularly interesting island.*) 



If we take a wider view of the geological features and the physical 

 outline of these just described high plains and plateaus consisting 

 of regular layers of trachytic rocks, breccia, and tuff, we shall find 

 that the steep cones of Ruapahu and Tongariro rise from the 

 centre of a vast tuff cone of extremely gradual inclination, the 

 basis of which occupies the whole country from shore to shore — 

 from East to West — having a diameter of 100 sea miles, and form- 

 ing the largest cone of tuffs, or in other words, the largest crater of 

 elevation in the whole world. 



The Hot Springs. 



Intimately connected with the described volcanic phenomena of 

 the active and extinct volcanic mountains, are the Solfataras, Fu- 

 maroles, and Hot Springs. They are found in a long series stretch- 

 ing across the country in a N. N. E. direction, from the active 

 crater Ngauruhoe in the Tongariro system, to the active crater of 



