72 Perner $ Kodym — Silurian of Bohemia. 



lock or Lower Ludlow age in Great Britain, or in cor- 

 responding strata in different Scandinavian districts ; but 

 as the limits of higher zones in all countries are not as 

 sharp as those of the lower ones, and hence the range of 

 many of the youngest graptolites is not everywhere coin- 

 cident, it would exceed the scope of the present communi- 

 cation to dwell longer on the particulars. Interesting 

 data along this line may be found in papers by J. Marr, 24 

 Lake, 25 E. M. R. Wood, 26 and G. Elles, 27 as regards the 

 British Silurian, and in the papers of Tullberg (1. c), 

 Munthe, Warburg, Hedstrom, Wiman, Moberg, 28 and 

 Kiaer 29 for Scandinavian districts. 



In spite of this, however, the graptolites are, generally 

 speaking, more reliable zonal guides than other groups in 

 these beds. Thus, for instance, the world-wide Cardiola 

 interrupt a appears already in E^ and survives until the 

 highest E 2 beds, while in other countries it is recorded up 

 to much higher beds than those of EjjS, and has a more 

 limited range. Further discussion on the correlation of 

 Bohemian beds will be deferred until more facts shall 

 have been gathered by new investigations. 



Prague, Czekoslovakia, July, 1921. 



24 Geol. Mag, 534, 1892. 



25 Quart. Jour. Geol. Soc, London, 51, 22, 1895. 

 28 Ibid., 56, 415, 1900. 



27 Ibid., 56, 370, 1900. 



28 For the five preceding authors see Guides for Excursions, Xlth Internat. 

 Geol. Cong., Stockholm, 19-22, 40, 1910. 



29 Videnskabs-selsk. skrifter, 2, Kristiania, 1908. 



