M. Barrande on the Silurian System of Bohemia. Ill 



genus, the Paradoxides, Brong., is also found in England and 

 Sweden, but no identical species have yet been observed. The 

 Agnostus is also common to all the three countries ; and the 

 Conocephalites of Bohemia seems to represent the Olenus of 

 Sweden and England. In the latter country some forms in 

 the oldest fossiliferous rocks show a strong analogy to those 

 of Bohemia. These are the few relations connecting this 

 Bohemian fauna with that of other lands, the genus Agnostus 

 being alone common to it and the Silurian rocks of Russia, 

 France, or the United States of America. 



Next in the ascending order is the stage of the quartzites, 

 D, so named from the predominance of a rock of this nature. 

 This deposit forms a long ellipse, extending from Rokitzan 

 almost to the Elbe, a distance of fifty English miles, with a 

 maximum breadth of eleven miles. It rests partly on the 

 former stage C, partly towards the SW. on the old azoic 

 rocks B, and is covered in the centre by the newer rocks 

 which it encloses as in a ring. Its vertical thickness is very 

 great. The lower parts consists predominantly of siliceous 

 rocks, — flinty slate, especially above the porphyries in the 

 NW. band of C ; siliceous conglomerates, particularly on the 

 SE. side of the axis ; and quartzites, sometimes composed of 

 distinct grains of quartz, cemented either by pure silica or 

 this mixed with clay, at other times presenting so fine a tex- 

 ture and such a brilliant vitreous aspect as to resemble 

 rather a chemical than a mechanical deposit. The beds vary 

 in thickness from a few centimetres to two metres, and are 

 divided by thin argillaceous or schistose layers, which seem 

 to mark periods of intermittance in the deposition of the 

 siliceous rocks. These interruptions have been sufficiently 

 long to divide the whole stage into concentric bands, running 

 the whole length of the basin, but, like the conglomerates, 

 thicker on the south-west. The alternating schistose rocks 

 form five principal masses, distinguished by peculiar charac- 

 ters. The upper three, near the top of the stage, are named 

 black laminated slates {Schistes noirsfeuilletes), very micaceous 

 slates {Schistes tresmicaces), and yellowish grey ^\sktQ^{Schistes 

 gris jaundtres)^ and are all collected near the top of the stage 

 in one mass, seldom under 1000 metres thick, and contain- 



