SECTIONS ON THE DONETZ. 
251 
into the Donetz, three versts from the village of the same name, lays bare on its 
banks a very instructive succession. In the upper part are courses of sub-con- 
cretionary or brecciated white limestone with Terebratulse, resting upon an agglo- 
merate of shells, and a band of very fine oolite : in the lower are yellowish cal- 
careous sands, or rather disintegrating sandy limestones, with ferruginous oolite 
and yellow sand. The whole of these beds may have a thickness of about forty feet. 
The fine-grained oolite and the shelly agglomerate are the beds most worthy of 
attention, and they are also by far the most constant ; for we traced them north- 
wards by Izium to Donetzkaya near the military colony of Petrofskaya. The shelly 
beds contain in great abundance the Trigonia clavellata., a small Ostrea, Nerinsea, 
Astarte, Terebratula, and a Turbinolia. To these beds at Kamenka, and a little 
higher up the Donetz, lower beds of friable and soft limestone succeed, reposing 
upon ferruginous sandstone with plants and some lignite, which have been observed 
in one point only, and described by Major Blode. We did not see the plants in 
question, which ought to be compared with the recently discovered flora of the 
ferruginous sandstone of Moscow. Judging from their position beneath these 
white fossiliferous or Upper Jura limestones, there can however, we conceive, 
exist but little doubt, that the lowest beds on the Donetz are the equivalents of 
the highest beds at Moscow, or sands above the Oxford clay. Ihey are, therefore, 
of high interest in bringing the Jurassic series of North and South Russia into 
geological connection. 
The presence of the Nerinsea and of a coral unknown in the other Jurassic 
formations of Russia, the absence of Belemnites and the great scarcity of Am- 
monites (we shall presently, however, allude to a striking species), are points 
which seem to indicate a very notable change in the distribution of the fossils of 
the Jurassic epoch, so regular and uniform in all the central and northern parts of 
Russia. . . 
The most instructive of the sections on the Donetz in ascending order 
is certainly that of Izium ; for. besides affording a very complete development ol 
the uppermost Jurassic division, it also clearly shows that a considerable thickness 
of sand and sandstone (greensand) is there interposed between the Upper Jura and 
the white chalk In this section the inferior beds are not visible beneath the river 
alluvia, and the ascending order commences with the fine-grained oolite, the shelly 
agglomerate with Trigonia clavellata, and a compact hard limestone. The succession 
is explained in the accompanying diagram. The uppermost Jurassic strata are 
divisible, it will be observed, into live beds, each peculiarly characterized, and the 
