6Q6 



baerande's " colonies" in 



deposits. To this intrusive fauna he has given the name of " a colony," 

 a name somewhat ambiguous, perhaps, yet which faithfully expresses 

 one part of his theory, namely, that we have here an exemplification of 

 a contemporaneous fauna, nearly allied to his third fauna E, or the 

 Upper Silurian, which during the deposition of the strata D, obtained 

 for a time a settlement within the Bohemian area, and was afterwards 

 expelled, to reappear, after a lapse of ages, under a slightly altered 

 aspect. The following is a copy of the section by which M. Bari'ande 

 illustrates this doctrine of colonies, which, so far as relates to the geo- 

 logical sequence and position of the rocks, I have verified on the spot. 



Section through the basin-shaped Silurian Strata of the Centre of 

 Bohemia. — Barram^e. 



Fig. 7. 



D. Lower Silurian, with fossils of the 2d fauna of Barrande, coeval with Llandeilo flags of 

 Murchison. 



d\ to d 5. Subdivision of the same. 

 El. Colony or intercalated beds, with fossils specifically identical, for the most part, with 



those of E 2. 

 E2. ^ 

 F f 

 Q V Subdivisions of the Upper Silurian, with fossils of the 8d fauna of Barrande, 



H*. J 



t. Trap of contemporaneous origin with E 2, and of which some also occur in the 

 deposit E 1. 



It will be seen that the colony styled E by M. Barrande, but which I shall 

 call E 1, occurs in the midst of the strata d 4, one of the subdivisions 

 of D, so designated by Barrande. The fauna proper to E 1 contains 

 as may as 65 species, five of them peculiar, or not known elsewhere; 

 two common to the fauna of d 4, in which they are intercalated ; and 

 the remaining 58 common to the base of Barrande's third or Upper 

 Silurian fauna, which I have designated as E 2. 



The late Edward Forbes, when commenting on this doctrine of colo- 

 nies, observed that if accepted it would materially affect the value of 

 the evidence of organic remains, as determining the age and sequence 

 of geological formations, since the proposition involves the introduction 

 of a group of species that experience has shown normally to belong to 

 a later and distinct formation, not merely among and mixed with the 

 fauna of an earlier stage, but amid and separate from that fauna.'''* Pro- 

 fessor Forbes, therefore, while expressing the highest admiration of M. Bar- 

 rande's talents and labors, questions the accuracy of his geological facts, 

 remarkino; " that in a disturbed Silurian country where the strata lie at 



Quart. Geo!. Journ., 1854, vol. x. p. xxxiv. 



