110 M. Barrande on the Silurian System of Bohemia, 



author considers these as at least identical in age, and per- 

 haps even connected below the newer beds. They both seem 

 to thin out towards the NE. extremity of the basin, and are 

 only well seen in a few deep river gorges. Thus the band of 

 Ginetz, though from 300 to 400 metres thick, is yet intercal- 

 ated between such enormous masses of quartzites and con- 

 glomerates, as almost to disappear. In consequence of the 

 degradation of the surface, the soft slates have formed a 

 longitudinal valley between high and steep escarpements of 

 the harder masses, and these at length yielding to the in- 

 fluence of the atmosphere, have covered up the slates with 

 a great thickness of siliceous ruins. When to this is added 

 the vegetable soil formed under the shade of the primeval 

 forests that still flourish on the mountains of the Trzemoschna 

 and Brdi- Wald, it will be easily seen that the labour of the 

 geologist, in tracing out these deposits, is by no means light. 



These beds contain a distinct group of organic remains, 

 which M. Barrande regards as the primordial fauna of 

 Bohemia. This fauna contains Trilobites in abundance, some 

 forms of the family of Cystidese, and a few species of Orthis. 

 The other classes are not represented. Now, among the 

 Trilobites, the dominant forms of that early creation, it is re- 

 markable, that not only all the species, but all the generic 

 types except the genus Agnostus, belong to it exclusively, and 

 do not live on into the higher stages. This is true also of the 

 species of the Cystidese and Orthis found in stage C, which thus 

 exhibits almost no connection with the other Silurian forma- 

 tions. Hence some event must have caused either the sudden 

 extinction or the emigration of the myriads of Crustacese 

 which swarmed in this sea. In the NW. band, masses of 

 porphyry are seen in the vicinity of Skrey, alternating with 

 the upper part of the formation, and changing the character 

 of the rocks. This eruption of igneous matter spreading out 

 over the bottom of the sea, may not only have destroyed life 

 there, but the deleterious influence of the substances thrown 

 into the water may have produced the same eff^ect on the 

 south-eastern band. 



The two bands contain twenty-five species of Trilobites, 

 of which five are common, ranged under seven genera. One 



