JURASSIC BASIN OF THE MIDDLE VOLGA. 
231 
the lines of bedding, and is rich in Ammonites and Belemnites. Towards the 
base of the formation only, are found some continuous beds of an impure are- 
naceous limestone. As far as I can determine the fossils, they seem to me all to 
belong to the middle Jura ( Terrain Oxfordien). The Belemnites excentricus, and the 
forms which approach that species, such as B. Puzotianus, B. Beaumontianus, are 
the most frequent remains. On the river Cisola I also found the rib of a 
Saurian 
To demonstrate, however, the truth of our statement, that the Palaeozoic depo- 
sits are at once succeeded by strata of the age of the Oxford formation, we now 
pass to the detailed desci’iption of these Jurassic masses, in the chief tracts where 
we examined them daring the years 1840 and 1841. 
Jurassic Basin of the Middle Volga. — We will first describe the strata of this age 
which occur midway upon the course of the Volga, because being there, as we 
believe, incumbent on rocks of less antiquity than in the other part of Central 
Russia, in which we could detect a junction, an ascending series might be best 
looked for, which, if any such passage existed, would show the connection between 
the Paleozoic and secondary formations. To the east of Kostroma the V olga 
winds, as already described (p. 178), through masses of red sandstone and marl, 
which we are unable to separate from the Permian system. In the greater part 
of this tract, the substrata are obscured by a thick cover of detritus, which 
is chiefly composed of the regenerated materials of the adjacent red rocks. But at 
about eight versts north-west of the village of Crasnoe Pojeni, deep red and finely 
laminated beds with geodes of harder marlstone, to which allusion has been 
already made, are seen to rise upon the right bank of the Volga to the height of 
thirty feet above the stream. These beds are surmounted, and as it then appeared 
to us, in perfect conformity, by dark-coloured (greenish black) clay, in which 
occur small crystals of selenite and concretions of indigo-blue, argillaceous lime- 
stone. In the clay or shale, which is in absolute contact with the red rocks, we 
observed but few organic remains, though a large Belemnite was abundant. In 
other beds, however, which occur at intervals along the banks of the river, we 
found the Ammonites cordatus (Sow.), Turbo muricatus (Sow.), with several species of 
Belemnites, including the B. absolutus (Fischer), which M. D’Orbigny has idem 
tified with a species found in Oxford clay at the Vaches Noires in Normandy 1 2 . 
1 Letter of Count Keyserling to Mr. Murchison, 6th hjovember 1843. (See Map.) 
» The new species of Belemnites will be described by M. D’Orbigny in the Third Part of this work. 
2 H 2 
