BAfiRANDE COLONIES. O 



mined with certainty (p. 211) ; Lut it is possible that further research 

 in the Harz may sooner or later confirm the facts observed in Bohe- 

 mia, of the sporadic appearance of fishes towards the close of the 

 Silurian period, along with Dalmanites, Bronteus, Acidaspis, and other 

 types characteristic of zone G (p. 212). Moreover, it is possible that 

 the deposits of the Harz form part of the great Palaeozoic zone of the 

 north like those of the environs of Hof, and were separated from the 

 Bohemian basin by an ancient barrier of gneiss and other crystaUine 

 rocks. In Spain, Sardinia, and France no beds higher than zone E have 

 been observed, unless it is in the department of the Lower Loire, 

 where M. Cailliaud has observed the coexistence of several species 

 characteristic of stage P, with others considered as Devonian. 



Crossing the Atlantic, M. Barrande considers the North American 

 representatives of his third division of the Silurian system, and 

 arrives at somewhat different conclusions from those drawn by MM. 

 de Yerneuil, D. Sharpe, and Hall. Excluding the Clinton and Medina 

 groups as passage-beds between the two great divisions of the system, 

 he includes the Niagara group and the whole of the Lower Helder- 

 berg series as representing his zone E. Zone E is represented by the 

 Oriskany Sandstone, the remaining members of the upper Helderberg 

 series being regarded as representing generally zones G and H ; and 

 he considers that, by means of certain Devonian forms in the Upper 

 Helderberg series, these beds are more intimately connected with the 

 Devonian system of Europe than are those of Bohemia, which contain 

 a smaller number of Devonian types. 



Eecapitulating his facts, M. Barrande observes that the countries 

 in the neighbourhood of Bohemia, namely. Saxony, Thuringia, and 

 Franconia, do not present a single trace of the last phase of the third 

 fauna, but that the first phase of this fauna is distinctly recognized. 

 The Silurian rocks of these countries appear to belong to the great 

 northern Palaeozoic zone, like England, Russia, and the Harz, the 

 faunas of which present us with more marked connexions with the 

 phase of life appertaining to zones G and H. 



Norway and Sweden, which belong to the same northern zone, and 

 are intimately related to England by the character of the earlier por- 

 tions of its Upper Silurian fauna, present none of the phases of 

 the latter part of that period. France, Spain, and Sardinia on the 

 contrary, although forming, like Bohemia, part of the great central 

 Palaeozoic zone, and presenting the earher phase of the third fauna, 

 are equally devoid of the latter portion ; but there are beds, considered 

 in France as representing the Lower Devonian system, which contain 

 fossils similar to forms disseminated through zones E, F, and G. 



In England, the Isle of Oesel, and the Harz, zones G and H ap- 

 pear to be partially represented. In the Upper Ludlow and passage- 

 beds of England we find six genera of fishes associated with fossils 

 of Silurian types ; but the Trilobites Dalmanites and Bronteus, and 

 the Cephalopods with a contracted orifice, characteristic of the higher 

 beds of Bohemia, are absent, as also are the Goniatites and Cardiola 

 retrostriata. In the Isle of Oesel, where the number of fishes 

 amounts to 43 species, among which are Coccosteus and Asterolepis, 



