Summit of Mont Perdu, 367 



sioned some confusion in the results. At noon I noted 

 down the heights of the barometer and thermometer. The 

 corresponding operations were made at Tarbes : at that 

 place, the barometer, when every correction was made, 

 stood at 27 inches 1*47 line; and the thermometer, at 20*50 <> 

 of Reaumur. At the summit of the peak the barometer 

 was 18 inches 11*14 lines; and the thermometer at 5*50° 

 above the freezing point. The height given by calculating 

 these observations is about 72 metres, or 37 toises below 

 what is given by trigonometrical observations ; but this dif- 

 ference seems to have arisen from the stormy state of the 

 atmosphere : at least I think myself authorised to infer so, 

 from more than 600 operations of the same kind, at diffe- 

 rent heights, with a view to ascertain the nature, extent, 

 and influence which the different modifications of the at- 

 mosphere have on measures obtained by means of the baro- 

 meter. 



The peak is covered with snow- to its summit : this snow 

 is continued towards the north, and transformed into an 

 immense glacier, which descends by stories to the margin 

 of the lake; its vertical height being about 800 metres. 



On the south, however, the face of the peak is unco- 

 vered ; but this is occasioned not so much by the action of 

 heat as by its steepness : as the snow cannot adhere, it con- 

 tinually falls down from the top of the mountain on a slope 

 six or seven hundred metres below, where it forms a glacier 

 of such extent as to resist the direct and reverberated heat 

 to which it is exposed by its situation. 



The uncovered part of the mountain did not exhibit to 

 me any strata in their natural place: it is an accumulation 

 of ruins divided by time, macerated by the snow, buffeted by 

 the winds, and beaten by the thunder, of which the greater 

 part bears impressions. All these ruins belong to the cal- 

 careous kind of stones, compact and fcetid, which arc here 

 in 'alternation with shell stones. I examined them with 

 an attention suited to the importance given them by their 

 situation. They contain a smali quantity of fine sand, coals, 

 a little iron, and a fcetid cadaverous principle, which seems 

 to arise from a bitumen of an animal origin. 



This last conjecture is certainly well justified by the dread- 

 ful destruction of the marine animals which accompanied 

 the formation of these mountains. This fcetidity, there- 

 fore, is not exclusively annexed to the strata of marble 

 found here. It is observed on breaking gres, of which car- 

 bonate of lime constitutes the smallest part, in the same 

 manner as sand is found in marble^ in which one might 



scarcely 



