300 VARIETIES OF 8AXD3TONE. 



their uniform and continued horizontally was caused by- 

 alluvial soils, or at least by arenaceous tertiary strata. The 

 sands which in the Baltic provinces, and in all the north oi 

 Germany, cover coarse limestone and chalk, seem to justify 

 these systematic ideas, which have been extended to the 

 Sahara, and the steppes of Asia. But the observations 

 which, we have been able to collect, sufficiently prove that 

 both in the Old and the New "World, both plains, steppes, 

 and deserts contain numerous formations of different seras, 

 and that these formations often appear without being 

 covered by alluvial deposits. Jura limestone, gem-salt, 

 (plains of the Meta and Patagonia), and coal-sandstone, are 

 found in the Llanos of South America; quadersand- 

 stein,* a saliferous soil, beds of coal,f and limestone with 

 trilobites,J fill the vast plains of Louisiana and Canada. In 

 examining the specimens collected by the indefatigable 

 Caillaud in the Lybian desert and the Oasis of Siwa, we 

 recognize sandstone similar to that of Thebes ; fragments of 

 petrified dicotyledonous wood (from thirty to forty feet 

 long), with rudiments of branches and medullary concentric 

 layers, coming perhaps from tertiary sandstone with lig- 

 nites ; chalk with spatangi and anachytes, Jura limestone 

 with nummulites partly agatized ; another fine grained 

 limestone|| employed in the construction of the temple of 

 Jupiter Ammon (Omm-Beydah) ; and gem-salt with sulphur 

 and bitumen. These examples sufficiently prove that the 



* The forms of these rocks in walls and pyramids, or divided in rhom- 

 boid blocks, seems no doubt to indicate quadersandstein ; but the sand- 

 stone of the eastern declivity of the Rocky Mountains, in which the learned 

 traveller Mr. James, found salt-springs (licks), strata of gypsum, and no 

 coal, appear rather to belong to variegated sandstone (bunter sandstein). 



f This coal immediately covers, as in Belgium, the grauwacke, or 

 transition-sandstone. 



In the plains of the Upper Missouri the limestone is immediately 

 covered by a secondary limestone with turritulites, believed to be Jurassic, 

 while a limestone with gryphese, rich in lead-ore, and which I should have 

 believed to be still more ancient than oolitic limestone, and analogous to 

 lias, is described by Mr. James as lying above the most recent formation 

 of sandstone. Has this superposition been well ascertained? 



Formation of molassus. 



|| M. von Buch very reasonably inquires whether this statuary limestone, 

 which resembles Parian marble, and limestone become granular by 

 contact with the systematic granite of Predazzo, ig a modification of 



