M. Barrande on the Silurian System of Bohemia. 109 



semi-crystalline rocks mentioned above ; the higher, B, the 

 clay-slate. This rock is sometimes the fine grained clay- 

 slate, with alternations of flinty slate ; at other times it be- 

 comes more or less of a conglomerate. True conglomerates 

 also occur both in stage B, and in the two next higher stages, 

 C and D. They abound especially in the south-east of the 

 basin, almost to the exclusion of other rocks, and thence run 

 out along the central axis of the valley. Their vertical thick- 

 ness is also greatest on the south-west, rapidly diminishing 

 to the north-east, which is .likewise true of the whole deposit. 

 The size of the fragments too, decreases in the same direc- 

 tion, so that it may even be said that in the north-east third 

 of the basin there are no conglomerates, but only very fine 

 siliceous sandstones or quartzites. From these facts the 

 author concludes that this portion of the formation has been 

 deposited by currents running from south-west, parallel to 

 the axis of the basin, and debouching on the north-east into 

 the open Silurian sea. His facts seem rather to indicate a 

 delta deposit in a great gulf, the materials of the conglo- 

 merates being also found in the ancient rocks on the south- 

 west. Limestone only occurs in this part of the series in 

 veins, or in very rare and insignificant lenticular masses. In 

 the stage B, the two most important metalliferous districts of 

 Bohemia occur. The veins of argentiferous lead-ore, wrought 

 at Przibram, near the middle of the south-east side of the 

 basin, traversing the clay-slates and fine grained conglomer- 

 ates or greywackes. The mining district of Mies, on the 

 north-west side of the basin, is also in fine clay-slates inter- 

 calated with flinty slate. 



The next higher stage, C, is that of the protozoic schists, 

 distinguished from the inferior group principally by contain- 

 ing organic remains which have not been observed lower- 

 They are fine grained argillaceous slates, with a small pro- 

 portion of silica and oxide of iron, and very minute scales of 

 mica. Their colour is often green, like the Silurian rocks of 

 England, but becomes brown on decomposition, when some 

 of them also separate into spheroidal crusts. This group is 

 only found in two detached portions, one on the NW. side of 

 the axis near Skrey, the other on the SE. at Ginetz, but the 



