114 M. Barrande on the Silurian System of Bohemia. 



so that only nine genera continue upwards. The author, 

 when he published his Preliminary Notice in 1846, knew of 

 no species common to this and the higher division ; but his 

 attention having been drawn to the occurrence of such transi- 

 tional forms in England by Sir E,. Murchison, he made more 

 diligent search, and now is acquainted with 20 well deter- 

 mined species which pass from the lower to the upper divi- 

 sion of the Silurian formations. This is an important fact, 

 as confirming the truth, now so apparent from the researches 

 of English geologists, that the Silurian formations compose 

 a great natural system, which cannot be divided without ex- 

 treme violence. That the Bohemian quartzite strata belong 

 to the lower division of the system is shewn by several cha- 

 racters : First, by the presence of the following genera of 

 Trilobites, Agnostus^ Asaphus, Bemopleurides, Dindymene^ 

 Illcenus, Trinucleus, Ampyx, all characteristic lower Silurian 

 forms, though the last three also appear in the bottom of the 

 upper division ; second, by the great development of Orthis, 

 as also happens in England, Russia, and North America ; 

 third, by the masses of Cystidese analogous to those in the 

 lower Silurians of the above countries, and also of Sweden 

 and Ireland. There is thus a great harmony in the Silurian 

 life of these distant regions, but with a few points of differ- 

 ence. Thus, in North America, and partly also in Scandi- 

 navia and Russia, Cephalopods greatly predominate in this 

 division, especially forms of Orthoceratites with a large 

 siphon, which are entirely unknown in Bohemia, in Britain, 

 and in France. In many respects these Bohemian quartzites 

 are most analogous to the Caradoc sandstones of England.* 

 The analogy of this lower division of the Bohemian rocks to 

 the Silurian formations of Scotland is also very remarkable, 

 especially in their physical and petrographical characters. 



These rocks compose the lower division of the Silurian 

 rocks of Bohemia. The upper division forms only as it were 

 a small oval ,island rising above their surface, and extending 



* The following species are noted from both deposits : Trinucleus ornatus, 

 Stern, lllcenus perovalis, Murch. Orthis redux, Barr. 0. testudinaria, Murch. 

 Orthis compressa, Murch. Bellerojphon acutus, Murch. The Lingula attenuata, 

 Murch., from the Llandeilo Flags is also found in the Bohemian quartzites. 



