S90 
VAKIETIES OF SAITDSTOIfE. 
their uniform and continued horizoutality was caused bj 
alluvial soils, or at least by arenaceous tertiary strata. The 
sands which in the Ealtic provinces, and in all the north of 
Germany, cover coarse limestone and chalk, seem to justify 
tliese systematic ideas, which liave been extended to the 
Sahara, and the steppes of Asia. But the observations 
I 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 bein" 
covered by alluvial deposits. Jura limestone, gem-salt, 
(plains of the IMota and Patagonia), and coal-sandstone, are 
found in the Llanos of South America ; quadersand- 
stein,* * * § a saliferous soil, beds of eoal,t 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, w© 
recognize sandstone similar to that of Thebes ; fragments of 
petriiied dicotyledonous wood (from thirty to forty feet 
^ong), 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 
limestonejl employed in the construction of the temple of 
Jupitm' Ammon (*Omm-Beydah) ; and gem-salt with sidphur 
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 whiirh the learned 
traveller Mr. James, found salt-springs (licks), strata of gypsum, and no 
coal, appear rather to belong to variegated sandstone (banter sandstein). 
+ This coal immediately covers, as in Belgium, the grauwacke, dr 
transition -sandstone. 
X In the jdains of the Upper Missouri the lime-stone is immediafely 
covered by a secondary limestone with turritiilites, believed to be Jurassic, 
while a limestone with grypheae, rich in lead-ore, and which I should have 
believed to he still more aTieient than oolitic limestone, and analogous to 
lias, is described by Mr. James as lying above the most recent formation 
of sandstone. Has ttiis superposition been well ascertained? 
§ Formation of molassus. 
II M. von Buch very reasonably inquires whether this .statuary limestone, 
which resembles Parian marble, and limestone become granular by 
coutact with the systematic granite of Predazzo, is a modification of 
