SECTIONS OF WHITE LIMESTONE ON THE OKA. 
81 
woodcut, the lower strata are composed of the excellent white limestone of which 
Moscow is chiefly built, surmounted by beds of a compact, yellow magnesian lime- 
stone with flat and conchoidal fracture, and often a pure dolomite without the 
appearance of crystalline structure. 
At Pudolsk on the river Pakra, the uppermost beds of the white limestone con- 
tain a little chert, and have in parts a coarse oolitic structure. These rest upon 
a thicker bedded rock, with courses of flint and some magnesian strata of a cavern- 
ous nature. It w r ould thus appear, that the white limestone alternates with mag- 
nesian bands, for at Miatchkova they overlie, and here they underlie that rock. 
We have already described magnesian limestones of the Devonian age, and in 
addition to their great frequencvin the carboniferous rocks we shall hereafter point 
out their prevalence in an overlying system. 
Though very generally preserving its most characteristic fossils, the Spirifer 
Mosquensis (Fisch.), P. punctatus, P. antiquatus, and P. lobatus (Sow.), this rock 
changes its lithological associations in different places. We have already alluded 
to the occurrence of red and green marls with the limestone on the route to 
Archangel. The same relations are seen at one spot on the banks of the Moskva, 
near Moscow, as pointed out to us by an English gentleman, Mr. Frears, long 
resident in that city \ Again, at Radionofka, twelve versts north of Serpuchof, a 
section in a ravine exposed a thin band of the white limestone, with Spirifer Mos- 
quensis, associated with flinty or cherty and yellowish bands, passing down into 
red and green marls with geodes of impure limestone, the whole based upon mica- 
ceous, incoherent, green sands. 
In fact, the prevalence of red and green marls, shales, and sands throughout the 
lower palaeozoic series, and in the overlying Permian deposits which we shall alter- 
wards describe, is one of the striking lithological features of Russian geology. 1 lie 
sections on the Oka, to which we now direct attention, are specially illustrative 
of this feature. 
Moscow Limestone on the Oka.— This central member of the carboniferous lime- 
stone is, perhaps, more fully exposed and with a greater variety of lithological fea- 
tures, on the banks of the river Oka between Serpuchof and Kolomna, than in any 
other part of the wide region over which it is spread. 
In descending this river from Serpuchof, some bands of white and grey, brown and 
■ In a subsequent chapter we shall speak of other researches of Mr. Frears, and of the instructive 
suites of Jurassic fossils which he collected around Moscow and kindly placed at our disposal. 
