78 
SECTIONS OF SAND, COAL AND LOWER LIMESTONE. 
of Stigmaria jicoides appear at intervals, whilst the impure and slightly consoli- 
dated coal is for the most part very pyritous, containing both sulphuret of iron 
minutely disseminated, and small geodes of crystallized pyrites. To show the 
slight persistence of any one of these coal seams, we may state, that in the bold 
cliffs of the Oka at Vornova, opposite Peremishl, they are represented (as on 
the Andoma, in the government of Olonetz, see p. 74) by a band of bituminous, 
stiff, black clay. This woodcut conveys a clear idea of the order, the sands and 
shale being covered by the Productus limestone. 
Near Alexina the coaly matter in the same strata expands so as to form layers 
subordinate to sands and shale. The thickness and relations of the coal-seams 
vary exceedingly in at least, forty localities, where they have recently been ex- 
plored by Colonel Olivieri. In all the chief points, however, he has invariably 
observed the same order of superposition as that which is conveyed in the above 
diagram, viz. sands, shale and coal, surmounted by the limestone with Productus 
giganteus. Most of these localities have been marked in detail by that officer on 
the map of Schubert, and we visited some of them with him. 
Throughout this region, as in the Valdai Hills, the coal is very pyritous, impure, 
fragile and light, and seldom equals in quality the best lignites of the Tertiary age 
in the Alps (Styria, &c.). We would account for the bad condition of this carbo- 
naceous matter, by the strata in which it lies not having assumed a lapidified con- 
dition, or having never undergone consolidation. The sands, in fact, are often 
as incoherent as the dunes of a sea-shore, the shale is mere blue clay, and the asso- 
ciated lignite is naturally light and impure, representing the first and second stages 
only in the chemical change which plants undergo in their transition into coal. 
Some seams, however, are superior in quality to others, from three to six feet 
thick, and presenting a natural outcrop in many ravines, the coal might be extracted 
14 . 
3. Sandy shale and sands. 
2. Bituminous black clay. In other places, coal. 
J. White sands. 
4. Strong-bedded limestone, with concretions of flint and 
containing Productus latissimus , Or this orach 
noidea, Euomphalua Dionysii, with several corals 
51. Snnrlv ennlo eovw4e 
Subsidences of limestone- 
