No. 2.] THE "colonies" of m. barrande. 191 



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 discon- 

 tinuous 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, regu- 

 larly 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 cZ 4, all the colonies are found 

 in the lower portion of c? 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, c? 4, & 6? 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 

 difi'ers most markedly botli from band e 1 and from the colonies ; 

 but nevertheless the palaeontological relationships of the colonial 

 zone are far stron";er with e 2 than with e 1, though the mineral 

 characters of e 1 are identical with those of the colonies. 



B. Band e 1 : — Band e 1 constitutes the stratigraphical base 

 of Etage E. or of the Upper Silurian Series of Bohemia. It 

 consists wholly of Graptolitic Schists, enclosing calcareous spher- 



