Dr Barry's Ascent to the Summit of' Mont Blanc. 115 



asbestos; and the fifth (D) a compound of hornblende and fel- 

 spar, one of the " Rochers a bulles vitreuses"" of De Saussure, 

 who attributed to lighinhig the glassy bubbles presented by 

 their surface. 



In our way down I procured specimens of the Derniers 

 Rochers (E), two little masses of granite or protogine, projecting 

 through the snow near the middle of the last slope, and there- 

 fore very near the summit on its north side. Fragments, doubt- 

 less the effect of lightning, lay around them on the snow. The 

 felspar, generally whitish, forms about three-fourths of the mass ; 

 the quartz is grey, with a tinge of violet ; and chlorite and talc 

 occupy almost exclusively the place of mica. De Saussure has 

 given a most minute description of the composition of these — 

 the highest rocks which at that time had been examined by na- 

 turalists ; — he stated also the dimensions of one of them, to 

 enable future travellers to ascertain whether the snow continued 

 to deepen on the summit. From what I recollect, this rock 

 projects just about as much now, as it did at the time of De 

 Saussiire's visit, which was nearly half a century ago. 



I intend sending specimens of all these rocks, marked as above, 

 to Professor Jameson, for the Royal Museum of Natural His- 

 tory in the University at Edinburgh. They are interesting, as 

 being the highest visible rocks in Europe. 



The observations of others were verified regarding the black- 

 ish-blue colour of the sky, particularly in and near the zenith, 

 as seen from these lofty regions. I was particularly struck with 

 the depth of this colour, when in a valley many hundred feet 

 below the summit, with high walls of snow around. It appears 

 to result from the simultaneous reception of rays from the snow, 

 for when the latter were purposely excluded from the eye, the 

 tinge of Much more or less completely disappeared. To make 

 this observation, I lay on my back, and closed my eyes for some 

 moments ; then opened them on the zenith, the snow being shut 

 out from view, by a cylinder formed with both hands. I do not 

 find a shade in " Werner's Nomenclature," corresponding with 

 the colour, as seen either with or without the snow ; and of course 

 it is not easy to speak from recollection on this subject ; but 

 probably an approach to the blackest tint observed might be 

 made by taking from " Pansy Purple" a little of its carmine 



H 2 



