MOUNT BOGDO. 
193 
beds of grey colour, containing Ostrese and Belemnites, and recently Colonel Hel- 
mersen has distinctly ascertained, that these strata are of the same age as the 
Jurassic formation, to which we shall presently advert as occurring in many parts 
of Russia. 
Mount Bogdo . — Having already stated, that we have no proof of the existence of 
rocks of the age of the Trias in the central region of Russia, it becomes our duty to 
ascertain, if there be not a representative of some member of that system in the rocks 
of Mount Bogdo, which rise up as isolated hills in the steppe of the inner horde of 
Kirghis, on the left bank of the Volga. 
No locality has undergone more changes in the estimate of its age than this 
famous mount, and it was therefore visited by one of us 1 with the view both of 
making a correct section and to collect the fossils which it contains The graphic 
description of Pallas, had the fossils which he collected been preserved, might 
have long ago enabled geologists to form nearly as accurate a conjecture concerning 
the age of these hills as that which we are now enabled to make ; for he informs 
us that their base, composed of saliferous masses, salt lakes, red and green sands, 
&c., is surmounted by limestone charged with shells and ammonites. 
Notwithstanding this ancient description, we find the most recent authorities 
exceedingly at variance in interpreting the age of these deposits. From an ex- 
amination of a chambered shell which they contain, M. Von Buch surmised that 
they might prove to belong to the Muschelkalk, and more recently Professor 
Eichwald has referred the deposit to the Silurian system ! 
We shall first endeavour to show that the latter opinion is untenable, and that, 
though not yet fully established, the opinion of M. Von Buch is much more likely 
to prove correct. 
Great and Little Bogdo . — The two contiguous hills of Bogdo are pretty nearly 
similar in composition. The little Bogdo is a low ridge stretching from north- 
north-east to south-south-west. At its northern extremity, a natural section exposes 
red sandstone dipping to the east at about 30°, surmounted by a whitish lime- 
stone, composed of angular, breccia-like fragments of a compact and hard nature, 
and forming masses so like ruined buildings, that the simple inhabitants seriously 
believe them to be such. The calcareous beds are covered by greyish coloured 
gypsum, and in their eastward dip, these strata are met and cut off by limestone 
Count Keyserling. 
