134 Prof. T. G. Bonney. On the [June 10, 



lying upon them. There are no rocks exposed at the immediate 

 summit. The highest rock we were able to obtain in situ was taken 

 from a small patch of glacier-crowned cliff, some hundreds of feet 

 below the central (and highest) peak on its western side, at a height 

 probably of about 18,800 feet. The culmination of the mountain is 

 an irregular ridge, several hundred yards long, having three distinct 

 snowy bosses." (E. W.) 



From the above-named lower summit the Pointe Jarrin Mr. 

 Whymper has brought nine specimens, two of which were broken 

 from rock in situ. Of the seven specimens collected from the 

 debris on the peak, two are rather scoriaceous : one, a small frag- 

 ment, is a whitish, rather glassy rock, containing small crystals of a 

 glassy felspar, with little plates of black mica and crystals of horn- 

 blende (?), in short, a very typical light- coloured "trachyte;" the 

 other is a rather denser rock with a pale reddish matrix and dull 

 whitish felspar crystals, containing apparently less mica or hornblende. 

 The other five are evidently varieties of a rock of the same general 

 character ; but one specimen is rather more micaceous than the rest. 

 The remaining four may be described as generally compact rocks, in 

 colour varying from a dull purplish to a reddish tint the latter 

 being probably due to an alteration in the iron constituent in fact, 

 I believe the differences in the colour to be mainly the results of 

 weathering. Fairly numerous crystals of whitish felspar, in diameter 

 from about 0'15 inch downwards, but generally not more than O'l inch, 

 are scattered in the matrix. I have examined microscopically two 

 specimens from the debris, and one of the two from the rock in situ. 

 I will describe first the most uniform looking and apparently 

 best preserved specimen from the debris ; a dull purplish-grey rock, 

 with a fair number of small crystals of whitish felspar, an unequal 

 fracture, and rather clean joint faces. The base is a clear glass, so 

 crowded with specks of opacite and ferrite and microliths of felspar 

 as to have a grey dusty look, except in the thinnest sections. In this 

 are scattered the usual crystals of felspar (plagioclastic, probably 

 labradorite) generally fairly free from inclusions. Magnesian silicates 

 are not very common, but I recognise both hornblende and augite, 

 the former (occurring as the larger crystals) being somewhat black 

 bordered and replaced by opacite, the latter clean and probably 

 belonging to a later epoch in the consolidation of the rock. There 

 are also to be seen scattered grains and crystals of magnetite and 

 perhaps of hematite. The rock has a general resemblance to some 

 of the higher fragments from Chimborazo. 



The next specimen (occasionally slightly vesicular, evidently a little 

 decomposed) is of a warm-red colour with crystals of glassy felspar 

 up to 0'2 inch, and a black mica, or hornblende, rather more con- 

 spicuous than in the rest. It bears a general resemblance to some of 



