GEOLOGY OF EREBUS 



Ross' original estimate of the height of Erebus may 

 have been correct, and this active volcano may have 

 gained in height by about a thousand feet during the 

 sixty-seven years which have elapsed since the time 

 of his expedition. In the next place among features of 

 geological interest may be mentioned the fact that the 

 old moraines left by a former gigantic ancestor of the 

 great ice barrier, ascend the western slopes of Erebus 

 to a height of fully 1000 ft. above sea-level. As the 

 adjacent McMurdo Sound is at least three hundred 

 fathoms deep, this ice sheet when at its maximum 

 development must have been at least 2800 ft. in thick- 

 ness. We noticed that in addition to these old ice barrier 

 moraines, there were moraines newer than the period of 

 greatest glaciation. They had evidently been formed by 

 glaciers radiating from Erebus. 



" As regards the geological structure of Erebus, we 

 have concluded provisionally that there is evidence of 

 the existence of four superimposed craters. The oldest 

 and lowest and, at the same time, the largest of these 

 attained an altitude of between 6000 and 7000 ft. 

 above sea-level, and was fully six miles in diameter. 

 The second rises to a height of 11,350 ft. and has a 

 diameter of over two miles; its rim is bounded inwards 

 by a vertical cliff, which no doubt descended originally 

 into a crater of vast depth. This second crater has now 

 been filled up almost to the brim, partly with snow, 

 partly with large crystals of felspar and fragments of 

 pumice, and partly with the numerous funnel-shaped 

 ice mounds already described. The third crater rises 

 to a height of fully 12,200 ft. above sea-level, and its 

 former outline has now been almost obliterated by the 

 material of the modern active cone and crater. The 

 latter, which rises about 800 ft. above the former, is 

 composed chiefly of fragments of pumice. These vary 

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