192 THE CANADIAN NATURALIST. [Vol. vi. 



oids or " antbracolites" and having intercalated beds of trap. Its 

 thickness is very variable, sometimes exceeding 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 palaeon- 

 tological differences between the two are sufficiently well marked, 

 though they are united by many specific connexions. Each, how- 

 ever, 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 sim- 

 ilar 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 palgeontologi- 

 cal 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 Etaii'e D., or the hio;hest 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 desti- 

 tute 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 appear- 

 ance of the "third fjiuna" (Upper Silurian fauna). In certain 

 localities, however, this unfossiliferous mass appears to have un- 

 dergone partial denudation^ prior to the dcp>osition of e\. 



It may be remarked here that the above observation ofM. 

 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 Ion 5, and cannot even be 

 approximately measured by the thickness of the upper part of 



db. 



Below this unfossiliferous series, band c? 5 is composed of masses 

 of argillaceous schist of different tints, sometimes with subordi- 



