54 
CENTRAL REGION OF DEVONIAN ROCKS. 
by detritus, it ranges from the environs of the latter place to near Orsha on the 
west and north, and thence is confluent with the western limits of the same deposits, 
to which we have already alluded as extending to the north-eastern frontier of 
Prussia. 
The general section from north to south across Russia, viz. from Petersburgh 
to the Sea of Azof (see below the Map), and which is carried through Moscow, 
Kaluga and Orel, gives a clear idea of the relations resulting from this great 
undulation, which separates Russia in Europe into two distinct geological basins. 
The northern basin, or that of Moscow, is included between these Devonian rocks 
in the centre, and those on the north which we have previously described ; and the 
southern extends to the rise of the carboniferous rocks and granitic axis of the 
southern steppes. By reference to the same section it will also be seen, that the 
northern basin consists, to a great extent, ot cai’boniferous limestone, with some 
patches of Jurassic rocks, and a fewspots of overlying, quartzose, tertiary sandstone ; 
whilst in the basin of the south (Kursk, Kharkof, &c.), the older rocks subside to a 
much greater depth, and the surface is occupied by a large development of Cre- 
taceous and Tertiary deposits. 
Having previously explained that the Devonian rocks of the Valdai Hills — those 
forming the northern limits of the basin of Moscow — pass upwards into the lowest 
beds of the Carboniferous system, we now proceed to point out the peculiarities of 
the central Devonian zone, and to show how, from its lower strata at Orel, it is 
composed of various beds, the highest of which dip under the rocks forming the 
southern limit of the carbonaceous basin of Moscow. In order of superposi- 
tion, and characteristic fossils, this central zone bears a close affinity to that 
of the North ; for it contains some of the same ichthyolites, with a profusion of 
Devonian shells, and is also surmounted by beds of limestone, charged with the 
Productus giganteus, which shell invariably occurs at the base of the carboniferous 
limestone. In lithological structure, however, it is scarcely possible that two de- 
posits of precisely the same age and relations, separated from each other only by 
a basin having the width, fi’om north to south, of about 300 miles, can present 
greater distinctions ; and this will appear the more remarkable, when it is stated, 
that in both cases (as indeed nearly all over Russia in Europe) the strata are 
unaltered. 
The central zone, of which we are now treating, is certainly as little entitled 
to the name of Old Red Sandstone as the black slaty rocks of Devonshire, for it 
