618 J. E. ITAEE ON THE PEEDEVONIAN 



the Primordial era, the rocks containing the Primordial fauna, as 

 well as the underlying conglomeratic series, being only locally de- 

 veloped, whilst it is not until the overlying beds of d 1 a that any 

 thing like continuous deposition appears to have set in. Again, if I 

 am right in referring d 1 a & /3 to the Lingula Flags and Tremadoc 

 Slates respectively, the unconformity between the Primordial zone 

 and second fauna of Eohemia does not occur at the same horizon as 

 that between the Primordial zone and overlying beds of Britain, for 

 the equivalents of d 1 a & /3 are included in the Primordial beds of 

 Britain, or Cambrian of Sir C. Lyell, Dr. Hicks, and Mr. Lapworth. 

 The break between the second and third faunas of Bohemia, on the 

 other hand, occurs at the same horizon as in Britain, viz. between 

 the top of the Bala beds and the Graptolitic fauna of Birkhill age. 

 Lastly, the beds of d 1 a & /3 have as yet yielded by no means a 

 satisfactory fauna, so that we do not here get one fauna in beds 

 imm.ediately succeeding another, as is the case with the beds at the 

 top of the second and base of the third faunas of M. Barrande. 



But the connecting link between these two latter periods was 

 supposed to have been discovered in the colonies of M. Barrande. T 

 feel justified in saying that I have brought forward sufficient evi- 

 dence to warrant a reconsideration of the data on which the theory 

 of colonies was founded, and to give some grounds for the supposition 

 that they are only portions of the band e 1 faulted down among the 

 grits and shales at the summit of the Cambrian series. 



Discussion. 



The Peesident said that Mr. Marr was the first person who had 

 attempted to correlate the Tremadoc, Arenig, and Bala beds of 

 Britain with those of Bohemia. It was very difficult to understand 

 the existence of these colonies. In Britain we have no recognized 

 colonies ; but repetition of species occurs in some of the Secondary 

 rocks. The lists of fossils contained in Mr. Marr's paper were of great 

 value. 



Prof. T. M'K. Hughes said that the difficulties under discussion 

 arose from not checking the palseontological by the stratigraphical evi- 

 dence, and thought that we had in Mr, Marr's paper a most valuable 

 contribution by a very competent observer. In considering the 

 question he would inquire (1) What is the ordinary manner of 

 appearance of the various forms of life ? and (2) Have we experience 

 in any clear .case of that exceptional mode of occurrence described 

 by the distinguished author of ' The Theory of the Colonies ' ? As to 

 (1), he thought that new genera and species came in gradually, 

 owing to changes in the conditions affecting life in adjoining areas, 

 and that, after a similar interval, whether measured by the thick- 

 ness of continuously deposited strata or by the thicl^ness of missing 

 deposits in the case of an unconformity, we observe about the same 

 kind of difference in the general facies of the forms of life. As to 

 (2), the appearance of a group of fossils resembling the group in 



