TABLE OF THE SUBDIVISIONS OF THE SILURIAN ROCKS OF BOHEMIA. Different crystalline rocks. Destitute of fossils. These are the "etages azoiques " d 1. Compact argillaceous schists, rarely metamorphic. d 2. Beds of quartzite " (i. e. greywacke), sometimes Black, argillaceous, and micaceous schists. Impure, very micaceous schists of different tints, Colonies, composed of graptolitie schists, with cal careous spheroids, associated with beds of trap. Compact limestone, black or dark gray, not fetid. of Barrande. Probably Lower Cam Primordial fauna," comprising 27 trilobites, 5 pteropods, 2 brachiopods, 47 trilobites. 25 cephalopods, 14 pteropods, few gasteropods, brachiopods, 19 trilobites, 1 cephalopod, 8 pteropods; other fossils very rare. 18 trilobites, 1 cephalopod, 10 pteropods. 8 trilobites and 9 brachiopods. 26 trilobites, 6 cephalopods. 18 pteropods; rare, gasteropods, brachiopods 4 trilobites, 36 cephalopods; few brachiopods; many graptolites. 15 trilobites, 149 cephalopods, 5 pteropods ; few gasteropods, brachiopods 81 trilobites. 665 cephalopods, 11 pteropods; very many gasteropods, 11 trilobites, 31 cephalopods, 2 pteropods (first Tentaculites); few gas- 4 fishes. 56 trilobites. 55 cephalopods, 10 pteropods; few gasteropods, 6 trilobites, 12 cephalopods, 3 pteropods (Tentaculites common); few bi- 3 trilobites, 86 cephalopods (14 Goniatites), 2 pteropods; few gasteropods, 2 trilobites. 13 cephalopods (3 Goniatites), 3 pteropods (Tentaculites com- II. DISTRIBUTION OF THE COLONIES. The colonial zone occupies a great part of the superficial area and vertical thickness of the band d 5, forming an elliptical zone or belt concentric with the calcareous rocks of the Upper Silurian basin. From this basin the colonial zone is generally separated by schists and quartzites, which form the summit of d 5, and which contain no fossils of an animal nature. On the surface of this zone the colonies are distributed in concentric but discontinuous lines, with irregular intervals between. Each colony is in the form of a lenticular mass, of which the length enormously exceeds the breadth and thickness; and the phenomena of their distribution and their relations to the surrounding rocks prove plainly that they cannot be explained by invoking the agency of mechanical disturbance or faults. Several interbedded traps are found in the colonial zone, regularly interstratified with the colonies, and similar beds are found in band e 1 at the base of Etage E. They all have the form of elongated lenticular masses thinning out at both extremities. As the Silurian rocks of Bohemia form a basin, the colonies are, as a matter of course, found on both sides of the central group of calcareous rocks (Upper Silurian). With the exception of the "Colony Zippe," which is found in d 4, all the colonies are found in the lower portion of d 5; and, like the rocks amongst which they are situated, they dip inwards towards the axis of the basin. III. LITHOLOGY OF THE COLONIES COMPARED WITH THAT OF BANDS e 1, e 2, d 4, & d 5: A. Band, e 2.—This band is the second subdivision of Etage E., and is composed mainly of continuous beds of limestone, often fetid, almost black in colour, and chiefly composed of the debris of Crinoids. The beds of limestone are separated by thin courses of impure shales containing a few graptolites. Lithologically e 2 differs most markedly both from band e 1 and from the colonies; but nevertheless the paleontological relationships of the colonial zone are far stronger with e 2 than with e 1, though the mineral characters of e 1 are identical with those of the colonies. It B. Band e 1:-Band e 1 constitutes the stratigraphical base of Etage E. or of the Upper Silurian Series of Bohemia. consists wholly of Graptolitic Schists, enclosing calcareous spher oids or "anthracolites" and having intercalated beds of trap. Its thickness is very variable, sometimes excceding 600 metres, and it is always much thicker than band e 2. Lithologically, therefore, as well as in possessing interbedded traps, e 1 differs greatly from e 2. In the same way, the palæontological differences between the two are sufficiently well marked, though they are united by many specific connexions. Each, however, has its own fauna, and the richness of the two is very unequal. Thus, e 1 possesses but 15 Trilobites, whilst e 2 has 81 species; e 1 has yielded no more than 149 Cephalopods, whilst e 2 has yielded the extraordinary number of 665 species; and similar differences are found in the Gasteropods, Bivalves, and Brachiopods. Still, the propriety of retaining e 1 and e 2 on the same stratigraphical horizon is shown by numerous palæontological relationships, amongst which may be mentioned the fact that 68 Cephalopods are common to the two divisions. C. Band d 5-Band d 5 underlies band e 1, and forms the summit of Etage D., or the highest division of the Lower Silurian Series of Bohemia. Its upper portion has a thickness of 100 metres and is composed of alternating thin beds of gray schist and quartzite (graywacke). It is remarkable in being wholly destitute of fossils of an animal nature, having yielded nothing more than a few "Fucoids". This thick deposit, therefore, corresponds with a prolonged and total intermission of the Silurian fauna of the Bohemia area. The thickness of this unfossiliferous formation might serve as an approximate measure of the time which elapsed between the last appearance of the colonial fauna and the definitive appearance of the "third fauna" (Upper Silurian fauna). In certain localities, however, this unfossiliferous mass appears to have undergone partial denudation, prior to the deposition of e 1. It may be remarked here that the above observation of M. Barrande would seem to indicate a want of conformity between Etage D. and Etage E., such as is found in many other countries between the Lower and Upper Silurian rocks. If this be so, the interval between the colonial fauna and the introduction of the third fauna may have been indefinitely long, and cannot even be approximately measured by the thickness of the upper part of d 5. Below this unfossiliferous series, band d 5 is composed of masses of argillaceous schist of different tints, sometimes with subordi nate beds of quartzite. In all cases, with the exception of the colony Zippe, the colonies are intercalated in this portion of d 5; and there are also numerous beds ("coulées") of trap at various horizons. As will be seen immediately, this portion of d 5 is chiefly distinguished from the beds of the colonies by the fact that the schists are almost wholly destitute of graptolites. D. The Colonies.-The colonies, as just remarked, are situated in the schistose lower portion of d 5, and they are lithologically absolutely undistinguishable from band e 1, consisting of graptolitic schists with calcareous concretions and interbedded traps. The following distinctions, however, may be noted as compared with e 1: 1. The thickness of the colonies is always much less than that of band e 1; and there are fewer alternations of the graptolitic schists with the traps. 2. Certain colonies are composed entirely of schists without traps. 3. In some colonies (e. g. Colony Haidinger and Colony Cotta) there are bands of gray schists and quartzites like those of d 5. 4. The calcareous concretions are generally rarer in the colonies than in the band e 1, and they even appear to be wanting in some colonies, especially in the deepest (e. g. in the Colony Haidinger.) E. Band d, 4:-This band is composed of impure schists, which are always highly micaceous and deeply coloured, brown, gray or black. Though fissile, they are much less homogeneous and papery (" feuillétes") than those which constitute the superior band d 5. Sometimes there are intercalated beds of quartzite, and occasionally there are interbedded sheets of trap. There is only one colony in d 4, namely the Colony Zippe, situated within the ramparts of Prague. This colony differs from all the rest by its being entirely composed of a lenticular mass of limestone, about 25 centimetres thick, intercalated in the midst of regular alternations of schist and quartzite. IV. PALEONTOLOGICAL RELATIONS OF THE COLONIES. From what has preceded, it is evident that stratigraphically the colouies belong to the Lower Silurian series, and we have now to enquire what relationships can be shown to subsist between the colonial fauna and the second and third fauna respectively. The specific connexions of the colonial fauna, when examined in de VOL. VI. E No. 2. tail, will then be found to be most close and intimate with the first phases of the third fauna (Upper Silurian), so that palæontologically the colonies must be regarded as truly Upper Silurian. This result will be brought out by a comparison of the fauna of the colonies with that of the Lower and Upper Silurian periods respectively : A. Specific connexions between the Colonies and the Second Fauna. As yet only two colonies are known in which there is any intermixture of the characteristic forms of the second fauna (Lower Silurian) with those of the colonial fauna, i. e. with those of the third fauna (Upper Silurian). Thus, out of seventeen species in the colony Zippe, there are four species representing the second fauna, with twelve species belonging to the third fauna. On the other hand, in the colony d'Archiac there are only two species of the third fauna (viz. Cardiola interrupta and Graptolites priodon ?). It is quite clear, therefore, that the colonial fauna, as a whole, has very slight connexion with the second or Lower Silurian fauna. B. Specific connexions between the Colonies and the Third Fauna. In showing the specific connexions between the colonies and the third or Upper Silurian fauna, it will be advisable to review briefly the different orders of fossils represented in the Silurian basin of Bohemia. a. Fishes. No traces of fishes have been detected in the colonies or in the whole of the Lower Silurian series, and their only indubitable remains occur in Etages F and G, which have hardly any connexion with the colonies. (Altogether five fishes have been discovered in the Upper Silurians of Bohemia, viz. Coccosteus primus, C. Agassizi, Asterolepis Bohemicus, Gompholepis Panderi, and Ctenacanthus Bohemicus.) b. Crustaceans.-These are principally trilobites. The trilobites of the colonies, not taking into account the four species of the second fauna, are referable to eight species and seven genera, all belonging to the third fauna. The trilobites are, therefore, very limited in number, and their paucity agrees perfectly with the small number of these crustaceans in the first phase of the third fauna, i. e. in e 1, in which only fifteen species are known. On the other hand d 5 and d 4 have together furnished about eighty trilobites peculiar to the last phases of the second fauna. The remaining Crustaceans of the colonial fauna are Pterygotus Bohemicus, Ceratiocaris inæqualis, Entomis migrans, and Apty |