Correlation of the Silurian of Bohemia. 55 



Bande E x is composed chiefly of black graptolitic shales, 

 but becomes calcareous toward the top, passing into the 

 limestones of E 2 . This passage is marked by the appear- 

 ance of calcareous concretions (anthracolites) and thin 

 seams of bituminous limestones in the higher graptolitif- 

 erous shales. These intercalations become more numerous 

 toward the top of E 1? until the shales gradually dis- 

 appear and limestone-beds prevail, followed by thickly 

 bedded compact or crystalline limestones. The boundary 

 between Ej and E 2 , formerly uncertain, was proposed by 

 J. Jahn 7 almost wholly on the basis of petrography, and 

 the horizon of shales with concretions and limestone inter- 

 calations was classed as E 2 . I myself defined the same 

 boundary paleontologically, s taking the zone with Mono- 

 graptus colonus, M. dubius and M. roemeri as the highest 

 horizon of E^ This limit agrees in many localities with 

 the petrographic one of Jahn, and I compiled at the same 

 time a list of 230 more common molluscs, brachiopods, 

 and crustaceans, indicating their true horizon, E x or E 2 , 

 based on the new material collected from the chief expo- 

 sures zone by zone ; this will, I hope, aid in correcting the 

 designations in many collections abroad (see pp. 64-66). 



Bande E x . 



E 1? as now limited, can be divided into three chief subdi- 

 visions, which in general correspond to three "zones" 

 recognized by Marr, and for which I propose accordingly 

 (as in use for other Lower Paleozoic rocks of Bohemia) 

 the following designations : 



E x a = Diplograptus beds. 

 E x /3 = Priodon beds. 

 Ej-y = Dubius beds. 



About thirty years ago Jahn (1. c.) proposed to desig- 

 nate as E^ the graptolitic shales in which the calcareous 

 concretions are absent, and the upper part of Ej (shales 

 with concretions and limestone intercalations) as Ej/?. I 

 could not accept this purely lithological division, as it is 

 inaccurate and unreliable. As the far more reliable 

 graptolite fauna demonstrates in many sections, there are 

 shales containing Monograptus priodon, M. vomerinus, 

 Stomatograptus grandis, Cyrtograptus murchisoni, and 



7 Jahrb. d. geolog. Reichsanstalt, Wien, 42, 3, 1892. 



8 Bohemian Acad. Sci., Jubileum Memoirs, XX, 1915. 



