BARRANDE ON THE TRILOBITES OF BOHEMIA. 31 



II. Middle Division. 



This division offers two groups of rocks as distinct from one another 

 in mineral composition as they are in fossil contents. Their limits 

 are well-marked and they may easily be recognized in several localities, 

 especially along the abrupt cliffs which inclose the valley of the Li- 

 tawa, in the direction of Przibram towards Zditz. 



Group C— 1. Geological characters. — The beds of this group con- 

 sist almost exclusively of argillaceous schists, containing but a small 

 proportion of silex. They are fine-grained and readily distinguish- 

 able from those just described of the lower division, by the more or 

 less rounded form of the particles of which they are made up. They 

 have a decided colour varying from brown to blackish-blue, and ex- 

 hibit a laminated texture. The bedding can often be only discovered 

 by means of the fossils, as is the case with other schists. 



These beds are widely traceable, but are for the most part con- 

 cealed under those of the overlying deposit (D), which are greatly 

 thicker. The average thickness of this group is however nearly 

 400 yards. 



The spot where the edges of this formation are best exposed, is to 

 the right of Duschnik near Przibram. Schists are seen there suffi- 

 ciently resembling in appearance those we are now discussing, but 

 not containing any fossils. Descending the valley these are covered 

 up by quartzite, the order of superposition being very manifest. The 

 schists of this group at Duschnik dip nearly N.E., and extend to the 

 eastern extremity of the palaeozoic basin. 



Owing to disturbances and denudation, the fossiliferous schists 

 appear in two localities, Ginetz and Skrey, associated with and forced 

 up through the thick beds of the upper series (D). Both of these 

 localities have supplied several trilobites, but especially the latter, 

 which is situated about fourteen miles north of Ginetz. 



2. PalcEontological characters. — The fossils from these localities 

 include twenty-four species of trilobites, and contain scarcely any 

 other fossils. The general result of a comparison of these trilobites 

 with those of the Silurian rocks of other countries, appears to be as 

 follows : — 



1. Of the whole number, none are yet known to occur either in 

 France or Russia. 



2. If the Paradoxides Tessini, doubtfully quoted by Sir R. Mur- 

 chison* as a fossil of the Llandeilo flags of Wales, really occurs in these 

 beds, this highly characteristic species will be common to Bohemia 

 and Great Britain. The halves of Agnostus pisiformis, figured in 

 the ' Silurian System ' (pi. 25. fig. 6), have also the greatest resem- 

 blance to the author's Battus Orion^ and may be considered its equi- 

 valent. The mere fact that the genus Battus is represented in the 

 lower beds of Wales and also in Bohemia, is considered by the author 

 as sufficient to bring the two formations into relation, for this genus 

 is not known to extend vertically to a great height. Its position in 



* Memoir on the Palaeozoic deposits of Scandinavia, Quart. Geol. Journ., vol. i. 

 table p. 402. 



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