THE ORDOV1CI AN SYs'l KM 147 



Argillaceous facie*. 



IBrachiopod shales with Stauro- \ 

 eeplia/us I Leptsena limestone of Dalarne. 



Trinucleus shales ( T. anceps) ) 

 Zone of Climacograptus rugosus 

 Dicranograptus Clin- Chasmops limestone (C. mac- 

 gani rurus). 



x , ., Climacograptus Scharen- 1 

 f bergi / Be y ncl "a limestone. 



"a -j Diplograptus mucrona- j 



tus V Limestone with Ancistroceras. 



^ ,, Glossograptus Hincksi } 



-, Lst. with nisenus cenlaurus. 



Didymograptus geminus [ >' ^sapltus *nd Echino- 

 ,, Phyllograptus typus I 



,, Isograptus gibber ulus 

 , , Phyllograptus angusti- 

 folius 



,, Didymograptus balticus 

 , , Tetragrapti 



bites. 

 Megalaspis limbala 



and many Cephalo- 



pods. 

 Megalaspis planilim- 



bata, Niobe, and 



Symphysurus. 



There are several important points to be noticed in regard to this 

 sequence. The first is that the whole succession, though quite 

 complete and capable of minute subdivision, is only from 300 to 

 400 feet thick. The second point is that the beds are horizontal 

 and undisturbed. The third is that there is an upward passage 

 from the Cambrian (see p. 102) to the lowest bed which 

 can be classed as Arenig, so that the Swedish geologists prefer to 

 include the Tremadoc in the Ordovician System. Fourthly there 

 is the replacement of shales by limestones. 



In the Christiania and Westgothland districts, and in the 

 greater part of Scania, the Arenig and Llanvirn Series are 

 represented by the Lower Qraptolite shales about 150 feet thick, 

 but parts of these are replaced by limestone eastward till in Olaiul 

 the whole consists of limestone. This limestone formation is 

 generally known as the Orthoceras limestone from the abundance 

 of Orthoceratidse, and it is only in recent years that its complete 

 equivalence to the graptolitic shales has been established by 

 Moberg, Tornebohm, Hedstrom, and Wiman. 



In the same way the graptolitic shales with a Glenkiln species 

 are replaced eastward by an Ancistroceras limestone and a higher 

 band principally composed of the tests of Beyrichia (a small 

 Crustacean), while the Chasmops limestone is a still higher horizon 

 occurring in the Christiania district. 



In Scania the Bala Series is represented by shales with 



