248 
JURASSIC DEPOSITS SOUTH OF ORENBURG. 
conglomerate in situ, made up of similar materials resting on red Permian sandstone. 
It is probable, therefore, that all the rolled stones having the same characters which 
are spread over parts of the tract of the high steppe of Illetzkaya-Zastchita, have 
been derived from a disintegration of the Permian conglomerates which were re- 
arranged by the sea in which these Jurassic rocks were accumulated. Let this 
theoretical point be as it may, the lithological composition of the Jurassic rocks 
in the southern part of the government of Orenburg is highly interesting, in show- 
ing how similar mechanical submarine operations have been repeated in distant 
countries during former epochs, whenever the strata approach to hilly and disturbed 
tracts like the Ural, the surface of which has been much disturbed. In these strata, 
difleient as they are in their stony features from their equivalents in fossil contents 
thiough other parts of Russia, we see both siliceous and calcareous grits assimilating 
in aspect to certain beds of the Oxford oolite at Brora in the Highlands of Scotland 1 . 
Again, the conglomerate which appeared strange to those of our party who had 
only observed the Jura beds of northern and central Russia, has also its analogy to 
certain conglomerates and grits, which in Britain mark the base of the oolitic series, 
in tracts where the vibrations of the surface have been intense, and where coarsely 
aggregated and detrital beds stand in the place of the finely laminated lias shale of 
other portions of the island 2 . 
Upper Jurassic Group in Southern Russia . — We have shown that a great axis of 
Devonian rocks divides central Russia into two zones of very different lithological 
composition (p. 5-b). To the south of this axis there are no traces of Jurassic strata 
resembling the great mass of those we have described, nor indeed can any con- 
siderable development of strata of this age be observed in journeying southwards 
until they are found to constitute, and under a very different mineral aspect, the 
rocky crest of the Crimsea. Visited by one of us for a short time only, we ne- 
cessarily leave the description of that remarkable peninsula to the able authors, 
M. Dubois, M. Huot, and M. Hommaire, who have so thoroughly explored it, the 
first of whom has permitted us to consign to our own map its chief geological 
features, as well as those of the Caucasus, from illustrations prepared by himself. 
1 See Geol. Trans. N. S. vol. ii. p. 296, siliceous grit of Braambury Hill. 
2 On the northern shores of the estuary of the Severn, Conybeare and Buckland were the first who made 
us acquainted with lias conglomerates, and Mr. Murchison detected similar rocks in the north-western 
Highlands of Scotland, alternating with true lias limestones. In the latter situation there are also white 
grits, which might very well be employed as millstones, like the Jurassic grits of Orenburg. (See Geol. 
Trans., 2nd Series, vol. i. p. 303, and vol. ii. p. 361.) 
