148 STRATIGRAPHICAL GEOLOGY 



Hartfell species of graptolites, but in Dalarne it is replaced by 

 a limestone full of Leptcena sericea. The brachiopod shales 

 appear to represent the Upper Bala or Ashgillian division, their 

 lower part in Scania consisting of a greenish argillaceous limestone 

 and the upper of blue flaggy shales. 



6. Russia 



Ordovician and Silurian rocks occupy a broad area along the 

 south side of the Gulf of Finland, both in the islands of Dago and 

 Oesel, and on the mainland as far east as the southern shore of 

 Lake Ladoga. Part of this area is shown in Fig. 10. The deposits 

 are chiefly limestones with soft marls and shales, quite unaltered 

 but slightly inclined to the south, and their total thickness is 

 about 300 feet. 30 The succession is as follows : 



Feet. 



J8- 



M7. 



Borkholm Beds (marls and limestone) 



40 

 50 

 30 

 100 

 40 

 30 

 10 

 30 



Balax 7. Lyckholm limestones (corals and trilobites) . 



I 6. Wesenberg limestone and marls 

 Llandilo j 5. Jewe limestones and shale, Chasmops bucculcnta 



and -j 4. Limestones with Chasmops Odini . 

 Llanvirn (3. Echinosphserites limestone .... 

 . . /2. Vaginatus limestone (Orthoceras vaginatus] 

 ' m >\ 1. Glauconitic limestone with Megalaspis . 



Of these beds Nos. 1 and 2 correspond with the lower part of the 

 Orthoceras limestone of Sweden, and the next three with its 

 upper part. The age of No. 6 is uncertain, but it contains species 

 of Chasmops and Encrinurus. The higher beds represent the 

 Trinucleus shales and Leptsena limestone. It will be seen that 

 the whole series is essentially calcareous and just as condensed as 

 the Swedish facies, having evidently been formed very slowly in 

 clear water and far from land. 



E. CONDITIONS OF FORMATION 



From the facts mentioned in the preceding pages it may be 

 inferred that so far as the European region is concerned the 

 geographical conditions of Ordovician time were on the whole 

 similar to those of Cambrian time. Scandinavia and Russia were 

 still farther removed from any large tract of land, and the 

 continued slow subsidence of that area favoured the continual 

 deposition of fine mud or the formation of shelly limestones in 

 water of considerable but not oceanic depth. 



The much greater thickness of deposit in Bohemia shows that 

 in passing southwards we approach one of the larger Ordovician 



