42 
DEVONIAN ROCKS SOUTH OF ST. PETERSBURGH — LOWER BEDS. 
burgh to Moscow natural sections are very scarce, but the lower members of the 
system are observable in the water-courses of the little rivers Kerist and Polist. 
For some versts, indeed, to the north of the former, the surface of the soil begins 
to assume a reddish tint, and in the purple and grey limestones recently extracted 
for the use of the chaussee, we found remains both of shells and fossil fishes 1 . At 
Tchudova, 112 versts south of St. Petersburgh, both banks of the Kerist, particu- 
larly below the bridge, exhibit flag-like, compact limestones, which are from one 
to three inches thick ; the upper or lower beds of whitish cream-colour, and the 
central of a reddish hue, have a more concretionary structure. The surfaces of 
these calcareous flagstones convey the idea of their having originated in a sedi- 
ment which had been accumulated in a tranquil sea ; for they are crossed with 
fucoids and other peculiar bodies, whilst Mollusca and Encrinites are arranged 
along the fine laminae of deposit. 
The shells are unquestionably of Devonian age ; such as Serpula omphalodes 
(Goldf.), Spirifer muralis (nob.), 8. speciosus (S. micropterus according to V. Buch), 
8. Archiaci (Murch.), 8. granosus (nob.), Terebratula ventilabrum (Phill.) , Orthis 
striatula (Schloth.), 0. rnicans (V. Buch), O. crenistria (Phill.), Bellerophon armatus 
(nob.), together with cylindrical, branching, indeterminable bodies, fucoids?, and 
remains of Encrinites and Pentacrinites. 
These strata at and to the north of Tchudova may be classed as the lowest mem- 
bers of the Devonian system. At Kalapi-polist, a hamlet some versts to the south- 
south-east, other beds, which, from the general slight inclination of the strata, and 
the gentle rise of the country to the south, must be overlying, are detected in 
ancient quarries on the right bank of the Polist. They consist of finely lami- 
nated, red and cream-coloured, flaggy limestones, in parts compact, in parts more 
sandy, and showing a strong tendency to concretionary structure. The concretions 
are of a more or less compact, argillaceous limestone, having a sandier base of dark 
green, ochreous and reddish colours. In parts these concretions resemble some 
varieties of the Herefordshire cornstone, from which form they graduate on the 
one hand into micaceous, greenish sand and sandstone, and on the other into 
calcareous flagstone. Nests of calcareous spar are not unfrequent, and fucoid- 
1 Upon our last return from Moscow, late in the season, and when we were too much hurried to quit 
the chaussee, we examined numerous heaps of fresh-quarried, red, calcareous, shelly flagstone, recently 
discovered in the ravines north of Tchudova, in which were some large fishes’ scales ( G/yptosteus reticu- 
latus, Agass.) with true Devonian shells. 
