362 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Apr. 22, 



and detect recognizable fossils, why then my datum-line as to the 

 first appearance of invertebrate animals will of course be lowered, 

 and I shall bow, as I have always hitherto done, to palaeontological 

 faots. 



But to return to the ascending section of M. Giimbel. The summit 

 of the primary clay-slate, here reddish and chloritic, passes up into 

 quartzites, about 300 feet thick (2), containing Fucoids ; these are fol- 

 lowed by black siliceous roofing- slate (lydianstone or lydite), in which 

 fossils of the Primordial zone (1) occur, and among which M. Barrande 

 has detected the genera before mentioned. According to M. Bar- 

 rande, who examined them when I was at Prague, they consist of 

 Conooephali and Oleni, and also some species of Lingula, Orthis, 

 Discina, Pugiimculus, and fragments of Cystidece. 



In answer to a recent letter from myself, M. Barrande writes as 

 follows : — " This fauna (from the environs of Hof) presents evidently 

 Primordial characters by the predominance and the forms of its 

 Trilobites, which are accompanied by a small number only of the 

 usual Lower Silurian genera, i. e. Lingula and Discina, the Pteropod 

 Pugiimculus, and a Cystidean. 



i( The Trilobites predominate, indeed, over the other fossils, both 

 in the number of specie's and in the relative quantity of individuals. 

 I recognized eight to ten species of Conocephalus and Olenus, all 

 new, as well as another type which also seemed to me to be new. 

 With these Primordial Trilobites are also associated two or three 

 forms which everywhere characterize the Second Silurian fauna 

 (Llandeilo and Caradoc), i. e. Calymene and Cheirurus. 



" The coexistence of these different types is evident, since I found 

 them in the same piece of rock not larger than my hand. 



" The. occurrence of the genus Olenus, which is entirely absent in 

 Bohemia, and the appearances which the species of it present, 

 indicate that the fauna of the environs of Hof has more relation to 

 the English and northern zone than to the central zone of Europe. 

 There was, therefore, (of old) a gneissic barrier, more or less elevated, 

 between Bohemia and Bavaria, such as that which we now see. 



" I was drawing up an interesting parallel between these two 

 Palaeozoic basins ; but just as I was about to complete it, I was obliged 

 to quit Prague ; and since then I have been absorbed in very dif- 

 ferent occupations. 



" You will observe that the partial coexistence of the Primordial 

 and Second faunas on the frontier of Bohemia comes in very a pro- 

 jjos to aid us in the conception of the partial coexistence of the 

 Second and Third faunas in Bohemia, or, in other words, of my 

 ' Colonies.' " 



May I not add to this important notice of M. Barrande, that this 

 discovery near Hof links together, in a remarkable manner, the 

 lowest to the next succeeding member of the Silurian, and that this 

 band forms the natural base of that first great Trilobite -bearing 

 series, below which no recognizable Crustacean has yet ever been 

 found ? This Primordial zone is followed upwards by black siliceous 

 schists, 10,000 feet thick, all symmetrically and compactly arranged 



