282 STRATIGEAPHICAL GEOLOGY 



3. Limestones with Prod, giganteus. 



2. Sandstones, shales, and coal-seams ; some of the beds yield Prod. 



giganteus. 

 I. Sandstones and shales with lenticular limestones containing Prod. 



mesolobus. 



These beds are from 5000 to 6000 feet thick and appear to 

 represent both the Tournaisian and Visean stages. In the Donetz 

 area, according to Tschernyschew, nearly the whole series consists 

 of limestones. 



D. CONDITIONS OF DEPOSITION 



The geographical conditions which prevailed in the British area 

 during Avonian time are fully discussed in my Building of the 

 British Isles (3rd ed., 1911), but it will be useful here to extend 

 our view to those parts of the European region which have been 

 briefly mentioned in the preceding pages. 



The complete absence of any trace of Carboniferous strata in 

 Norway, Sweden, Lapland, and Finland seems to indicate the 

 existence of land over a large part of Northern Europe during this 

 period. This inference is confirmed by the character of the deposits 

 found in Northumberland, Scotland, and the north-east of Ireland ; 

 these being mainly detrital deposits carried down by rivers and 

 such as would be accumulated in a large bay or gulf. Hence we 

 conclude that the Scandinavian land extended westward across the 

 North Sea and across the north of Scotland into the North Atlantic 

 region. 



Again on the eastern side we find a broad band of Carboniferous 

 strata in Russia extending from the Valdai Hills, south-east of St. 

 Petersburg, northwards by the south end of Lake Onega. In this 

 band the lowest beds are terrigenous deposits similar to those 

 of Scotland, and here again, therefore, we are on the borders of 

 continental land. 



With regard to the southern border of the Scandinavian land 

 there is less certainty, because all evidences of it are buried and 

 concealed beneath the Neozoic deposits of the Germanic region. 

 Probably, however, the coast-line passed across the .southern part 

 of the North Sea and across Denmark into the Baltic basin, whence 

 it must have curved north-eastward through the Baltic provinces of 

 Russia. Here it may be pointed out that the absence of Avonian 

 deposits in Poland is no proof that this country was land at this 

 time. The Carboniferous deposits may have been largely removed 

 from that area before Permian time, and seeing the great thickness 

 which they have in Silesia and as far east as Cracow, it would be 



