623 



bites (Missoury above Council Bluff), fill the 

 vast plains of Louisiana and Canada. In ex- 

 amining the rocks which the indefatigable 

 Caillaud has collected in the Lybian desart, 

 and in the Oasis of Siwa, we recognize sand- 

 stone similar to that of Thebes ; fragments of 

 petrified dicotyledon wood (from 30 to 40 feet 

 long), with rudiments of branches and medul- 

 lary concentric layers, coming perhaps from 

 tertiary sandstone with lignites * ; chalk, with 

 spatanges and anachytes, limestone (jurassic) 

 with nummulites partly agatized; another 

 limestone with small grains -f- employed in the 

 construction of the temple of Jupiter Amnion 

 (Omm-Beydah) ; and gemsalt with sulphur and 

 bitumen %. These examples sufficiently prove 

 that the plains, (Llanos %) steppes, and desarts/ 

 have not that uniformity of tertiary rocks 

 which has been too generally supposed. Do 

 the fine pieces of ribboned-jasper, or pebbles of 

 Egypt, which M. Bonpland picked up in the 



* Formation of molassus. 



tM.de Buch justly enquires if this statuary limestone, 

 which resembles the marble cf Paros, and limestone become 

 granular by its contact with the systematic granite of Pre- 

 dazzo, is a modification of the limestone with nummulites of 

 Siwa ? The primitive mountains from which the marble 

 with small grains was believed to be extracted, if there is no 

 deception in its granular appearance, are far distant from 

 the Oasis of Siwa. 



X Caillaud et Drovetti, Voyage d Syouah, p. 8, 9, 16. 



