584 A. W. GRABATJ LOWER ORDOVICIC FORMATIONS 



BOHEMIA 



In portions of the Bohemian basin the Middle Cambric Skrej Jinetz 

 formation of Bohemia is followed with a marked discontinuity by the 

 sandstones of the Krusnahora formation (D 1 a), which are characterized 

 by Lingula feistmanteli. These beds have often been placed in the Upper 

 Cambric, but they are more properly classed as basal Ordovicic. Marr 

 considers that L. feistmanteli "is very near to the remarkable Lingula 

 roualti of the Armoricain grit." 18 He concludes that these beds are there- 

 fore late Arenig, the Lower Arenig and Tremadoc being absent in Bo- 

 hemia. 



The Krusnahora beds are quartzites, often glauconitic graywackes, 

 shales, and hornstones. These Krusnahora beds are absent throughout 

 the Jince district of the Bohemian basin, where the Paradoxides beds are 

 either followed by the ironstone-bearing zone of d 1 (3 or by d 2. 19 The 

 Lower Ordovicic division, which is most wide-spread in Bohemia, is the 

 Komorau formation or d 1 /3 of Barrande. This consists of black shales, 

 hematite ironstones, diabase, and diabase tuffs, the total not exceeding 

 •100 meters. It often overlaps the Krusnahora beds, resting directly on 

 the Middle Cambric. The fossils found in this formation include: 



OrtJiis desiderata Barr., 



Lingula, 



Harpides grimini, 



Amphion (Pliomcra) lindaueri, and 



Didymograptus (Isograptus) caduceus (Salter). 



The graptolite indicates Lower Deepkill for this series, and this is not 

 negatived by the other species. Marr would refer this division "'to a 

 position high up in the Arenig series." Here he would also place the 

 next succeeding Kvan-oseker beds d 1 y of Barrande, dark, mostly black 

 clay shales, and graywackes, with sandy intercalations. They contain : 



Placoparia zippei, Niohe discreta, 



Ogygia, Mglina prison , 



Asaphus nobilis, Rweiria, 



Illcenus lcatzeri, Orthis, and 



Bohemella, Didymograptus genii mis. 



Dalmanites, 



The graptolite marks this horizon as of Lower Llandeilo age, the hiatus 

 between it and the preceding Komorau formation (d 1 /?) including at 

 least Middle and Upper Arenig. These mid-Ordovicic beds are succeeded 



■ 1S Geol. Mag.. Sept.. 1889, decade iii, vol. vi, p. 413. 

 19 Jaroslav J. Jahn : Geologische Exkursion im Alteren Palseozoikum Mittelbohmens. 

 Fiihr. Cong. Geol. Int., IXe session, pp. 42-45 ; footnote. 



