56 
SECTION OF THE OKA — OREL. 
first, at Orel the following strata are seen in numerous large quarries on the right 
bank of the Oka to the south of the town : — 
jpi. in. 
1 1 . Sandy and shattcry tilestoncs of white colours, with yellow, compact marlstone 3 0 
10. Green and grey marl 4 o 
9 - Sandstone, for the most part incoherent, but occasionally hard, and of bright green, yellow and ferru- 
ginous colours. (One of the subordinate courses of this stratum is a coarse iron grit, with minute 
concretions of iron ore (pisolitic iron) ) 12 0 
8. Impure yellowish, sandy limestone 15 0 
7. Thin-bedded, yellow and white limestone 9 0 
6. Small concretionary compact limestone, in a yellow, sandy, magnesian matrix. This rock, which is 
the chief building-stone of Orel, weathers to the rude, cavernous exterior before alluded to, and is 
laminated by blueish-grev and ferruginous, calcareous courses 12 0 
5 . Fawm or light, butt- coloured, saudy, finely -laminated, magnesian limestone in two or three beds only, 
the lamime marked by ochreous stripes 6 0 
4. Light grey, concretionary limestone, in parts cavernous, with crystals of calcareous spar 6 0 
3 . Yellow, thin, magnesian limestone 1 6 
2 . Marly, light-coloured limestone 1 6 
1 . Mottled indigo and yellow, hard limestone, used as paving-stone, with way-boards of black and whitish 
shale. The surface of this rock is sandy, and weathers to a ferruginous colour 4 0 
74 0 
The lowest beds offer numerous fragments of small ichthyolites, which we con- 
sider to be the same forms as those described in the lower Devonian strata near 
Prussino and Tchudova (. Diplopterus and Glyptosteus) . 
The beds exposed in other quarries east of the town (12, 13 and 14 of woodcut) 
represent a higher part of the formation, which extends over a considerable area, 
and is probably the same rock which occurs in the ravines west of Novazilskaya, 
the first post-station to the south of Orel. Here we found (under black earth and 
surface clay) beds of greyish, greenish and yellow marls or shales, with a sub- 
ordinate course of yellow, sandy, magnesian limestone, in all about 15 or 16 feet 
thick. Beneath these, the strata which are extensively quarried for use, consist of 
thin beds of limestone, varying in colour from deep yellow to almost pure white, 
and containing numerous fossils, among which we recognised Area Oreliana (nob.). 
This shell alone forms entire beds, together with the characteristic Serpula ompha- 
lodes, Natica spirata, a very small Orthoceratite and two species of Corals. 
In proceeding from Orel to the north, we met with proofs at every natural denu- 
dation of the continuance of the same system of strata ; and whilst the left bank 
of the Oka exhibited them in distant cliffs, we recognised them on the sides of 
