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ORIGIN OF SOME SALT SOURCES OF THE STEPPES. 
any other part of Russia, and the entire absence of palaeozoic forms 1 , seem to 
conspire with the order of the strata, to lead us to consider this limestone of the 
steppe of Astrakhan, as a stage in the geological series superior to the Permian 
system, and which has not been observed in any part of Russia properly so called 
(see Map). 
We are very far from believing that these upper beds are Jurassic, both because 
we have not found among them any of the fossils which characterize the strata of 
that age in Russia, and also because the limestone of Bogdo is very dissimilar to 
any beds of that epoch with which we are acquainted. 
If, after all, the exact geological horizon of the limestone of Mount Bogdo is 
uncertain, our researches have, we trust, limited the range of formations to 
which it can be referred ; for it is now ascertained to be younger than the great 
body of the Permian and older than the Jurassic strata. Looking, therefore, to the 
“ facies” and dominant character of the fossils, and seeing that the limestone in 
which they lie passes gradually downwards into saliferous rocks which form a 
part of the Permian system, we are disposed to approach very nearly to the opi- 
nion of M. Von Buch, and to think that if not the equivalent of the Muschelkalk, 
these beds must at all events approach to that age. 
Origin of the Suit of the Steppe of Astrakhan . — In previous chapters it has been 
shown, that salt sources rise out of different deposits in Russia, from the base of 
the Devonian system to the red rocks associated with the Zechstein ; and as the 
largest and best-developed masses of rock-salt are of the latter age, and the saline 
sources of the steppe of Astrakhan issue from the foot of Mount Bogdo, we 
believe that they have their origin in similar masses of rock-salt. It is, indeed, 
quite evident, that these and similar saline sources are due to subterranean 
causes of an ancient date, and are in no way dependent upon the recent desicca- 
tion and retreat of the Caspian Sea ; for it is only where the mounts of red sand- 
stone rise out in this wide plain, that permanent salt-springs are known. In 
other parts of the same steppe, abounding as the surface does in marine shells, 
the finest fresh water is obtained, by boring to a few feet into the sand and gravel. 
1 Although the Ammonites Bogdoanus has not serrated lobes, like those of the Ceratites of the Mus- 
chelkalk, and ought, according to strict generic definition, to be placed among the Goniatites, it offers, 
nevertheless, by the form of its chambers, a very strong analogy to the Ceratites. The inclination of the 
folds of the lobes towards the interior edge of the whorls, and their comparative narrowness, recall forcibly 
to the mind of the geologist the Ceratites nodosus of the Muschelkalk (see Part III.). 
