536 DOMAIN V. CALCAREOUS, 



" The rounded pebbles, which have been long 

 exposed to the air, have also outwardly assumed a 

 blackish ferruginous tint ; but those which are still 

 enclosed in the beds of sandstone have, like that, 

 a yellowish colour. I found none in it which 

 were not of a primitive nature ; and the most part 

 were of a very hard grey or reddish felspar, and 

 confusedly crystallised. They are then stones 

 which do not naturally possess a rounded form, 

 and which consequently only receive that they 

 have here, by rolling and the friction of the 

 waters. 



" All these sandstones effervesce with acids 

 but the ferruginous parts of the net much less 

 than the base itself. In like manner, if the sand- 

 stones which contain pebbles, and those which do 

 not, are compared, in the former will be found 

 more calcareous gluten, their coherence being 

 much more diminished by acids. On the very 

 summit of the mountain these sandstones are co- 

 vered by a grey shining slate, which exfoliates in 

 the air ; and descending from this same summit, 

 on the N. E., on the opposite side to the passage 

 of Fours, beds of sandstone will be observed ex- 

 actly similar, and which there divide of themselves 

 in small parallelepiped fragments."* 



