EXTENSION TO VITEGRA AND ARCHANGEL. 
73 
Western Europe, which they much more resemble than any varieties ot the chert 
of the mountain limestone. 
In treating of the Silurian strata near St. Petersburgh, we have before remarked 
that it was on the sides of the hills only, and in ravines of the hilly district, that 
small local dislocations were observable, and so is it in the Valdai Hills, where, 
although the gorges for the most part show beds perfectly horizontal (as in the 
woodcut, p. 71.), they also exhibit local disruptions, as on the Stolobna rivulet. 
The fossils which we collected at this place are the small Trilobite Otarion 
Eichwalcli (Fisch.), Orthoceratites ornatus ( Amplexus ornatus, Eichw.), Gervillia 
laminosa (Phill.), Bellerophon depressus (Eichw.), Avicula Valdaica (nob.), Solemya 
primceva (Phill.), Spirifer glaber (Sow.), Productus scabriculus (Sow.), P. latissimus 
(Sow.) a small variety, Terebratida hastata (Phill. var.), Orthis arachnoidea (Phill.), 
with Chcetetes radians, Lithostrotion, and other corals, several of which occur in 
England. It is worthy of remark, that in these magnesian beds, the fossils present 
their interior casts only, the surfaces of which are covered with small crystals of 
dolomite 1 . These sections of the tributaries of the Msta have been dwelt upon, 
because we nowhere else saw so good an ascending succession from the Devonian 
beds, through the overlying coal-bearing strata and the lower limestones. 
Extension to Vitegra. White Limestone of Archangel. — Before we trace the car- 
boniferous limestone over the great basin of Moscow, in which its central member 
is so much developed, we would first describe its range to the north-east. Ex- 
posed on the banks of the rivers Kolp and Suda, between Tichvin on the north- 
west and Tclierepovetz on the south-east, its northernmost limits range by Vitegra 
and the plateaus north of the Andoma. Rising to the surface throughout con- 
siderable flat tracts near Kargapol, it is continuous across the Onega, appears in 
force upon the Dwina to the south of Kholmogor, and passing that rivei, ex- 
tends by the north of the Pinega to Mezene, the capital of the country of the 
Samoiedes 2 . The southern limits of this limestone may be indistinctly traced at 
' The above observation applies very generally to all the crystalline limestones, largely charged with 
magnesia. The fossils which are obtained from the magnesian variety of the Mountain Limestone at 
Breedon Hill, Leicestershire, such as Productus, Orthis, and Spirifer, the latter having the spiral braclna 
beautifully preserved, occur only in the state of casts, having their surfaces coated with regular dolomitic 
crystals. The fossils of the Magnesian Limestone of Humbleton Hill, near Sunderland, are also found 
in the same state. 
2 Our knowledge of the extreme points to which this limestone extends on the north-east, beyond 
Mezene, as represented in the Map, has been very recently obtained by one of us (Count Keyserling) from 
the distinguished botanist and traveller M. Ruprecht. Dec. 1842. 
