:'.'.* , Prof. T. G. Bonney. On the [Nov. 27, 



and at the time of my partial ascents the crests of the ridges leading 

 to the highest point were coated fantastically with overhanging 

 cornices of snow and small glaciers. On the south side, such rocks as 

 could be seen in situ were a highly decomposed trachyte, which 

 externally bore an almost chalky-white appearance, with veins and 

 patches of lilacs and purples pervading it. On June 9, 1880, previous 

 to attempting to ascend the mountains from the north, I encamped 

 against a huge block of trachyte (15,446 feet), from which I took the 

 specimen A. The Carrels, on their ascent, brought from the highest- 

 rock visible, in situ (close to the summit), the specimen B, and also 

 four specimens of debris from the same spot." (E. W.) 



From Illiniza five specimens have been examined ; one from the site 

 of the camp on the north side, and four from the summit, whereof 

 one was from rock in situ. The first, A, is a moderately dark-grey, 

 slightly vesicular " trachyte," containing crystals of glassy felspar 

 sometimes (though rarely) nearly j inch diameter, and some small 

 flakes of black mica. A slice shows a base of clear glass thickly studded 

 with acicnlar microliths (probably in part at least felspar) and granules 

 of ferrite and opacite, so that when viewed with low powers it has 

 a brownish-grey, finely granular aspect. In this ground-mass are 

 scattered abundantly crystals of felspar varying from about '1 inch 

 downwards, together with very numerous lath-shaped crystallites often 

 about '004 long. The larger, as usual, appear to be closely allied to 

 labradorite. They have often externally a worn corroded or broken 

 look ; internally they vary much ; some are nearly clear, many have a 

 few microlithic enclosures or spots of brown glass, a few are very full 

 of irregular patches of the latter; zonal banding is often well exhibited. 

 There is a little brown mica, some very characteristic hornblende, also 

 brown-coloured, and a considerable quantity of granules and small 

 crystals of a pyroxenic mineral, some of which, I think, are mono- 

 clinic augite, but others appear to be orthorhombic, and are probably 

 hypersthene. There are the usual granules of magnetite, and some 

 minute colourless crystallites which may be apatite. The rock accord- 

 ingly is a horublendic augite-andesite, containing also some mica and 

 bypersthene. 



The specimens from the summit are moi'e scoriaceous and of a 

 redder colour. One (debris) is more compact than the others, and of 

 a dull brick-red colour, spotted with small crystals of whitish felspar. 

 The others are very similar, being a rough scoriaceous rock, containing 

 felspar crystals similar to but not quite so large as those of the rock 

 described above. In one is an irregular branching tube or vein, 

 coated with a dull greenish or brownish glass, which I suspect to be 

 a fulgurite. I have only had a slice cut from the specimen broken 

 from the rocl^ in situ (B). It is not in a good condition for examination, 

 but consists, so far as I can make out, of a ferrite-staiued glass, con- 



