214 GENERAL GEOLOGY 



second crater, parting with more moisture as it became chilled in its ascent, and so 

 produced the snowfall. On other occasions we observed that the summit of Erebus 

 was capped by snow-cloud which gathered on top of the mountain at a time when 

 the lower slopes were entirely free from cloud. This development of high-level 

 snow-cloud was often the precursor of a southerly or south-easterly blizzard. 



A reference has already been made in Chapter II., dealing with meteorology, 

 especially in regard to snowfall, to the du-ection of the sastrugi on the floor of this 

 second crater. They were found on March 9 to follow the direction of the blizzard 

 wind experienced on March 8. 



If now we continue the section across the second crater of Erebus at an altitude 

 of about 12,000 feet the base of the thu-d crater is reached. This lies a little to 

 the west of the present active crater. This third crater rises to about 12,600 feet 

 above sea-level. 



A little to the east of the third crater, which is extinct, is the present active 

 crater. The fourth and active crater of Erebus rises as a moderately steep cone 

 largely free fi'om snow and formed mainly of pumice. The latter is grey to yellowish 

 on the outside, and of a resinous brown appearance on freshly fractured surfaces. 

 The lumps were from about 1 inch up to about 3 feet in diameter. 



The spectacle afforded by the active crater is truly magnificent and inspiring. 

 The summit as determined by our hypsometer was about 13,300 feet above sea-level.* 

 The crater itself is a vast abyss fully half a mile in diameter and about 900 feet in 

 depth. Its walls are nearly vertical, with a suggestion of terracing due to the 

 presence of layers of unequal hardness. Plate LXIV. Fig. 2 shows about 200 feet of 

 this crater wall. The dijD of the beds of pumice and lava away from the crater can 

 be seen in the photograph. 



The view was taken looking towards the west through a great breach in the 

 crater rim. Evidently the latest flow of lava has descended in that direction. The 

 highest parts of the crater rim appear to be on the south and east. For the greater 

 part of the time of our visit a vast column of steam and sulphurous gas obscured 

 everything at the bottom of the crater. This rose many hundreds of feet into broad, 

 mushroom-shaped masses in the air above us. When the wind di'ifted the clouds 

 towards us the smell of sulphur was strong and almost overpowering. Every now 

 and then could be heard a roaring noise, like that of a huge engine blowing off 

 steam, coming from beneath the crater, and this was immediately followed by a 

 greatly increased uprush of steam. As we watched, a gentle northerly breeze 

 drove the steam cloud to the south, and enabled us to see across the crater and down 

 to the very bottom. We then made out that there were three well-like openings 

 giving off steam at the bottom of the great cauldron. The approximate position 

 of these is shown on the plan, Fig. 66. 



* The exact correction factors for hypsometers in such latitudes being uncertain, the deduced levels 

 are obviously also uncertain. 



