422 



In regard to the bearing of this stratigraphical question upon 

 the generalizations of paleontology, Prof. Rogers admitted that the 

 discovery of primordial forms at so high a level would be a re- 

 markable and exceptional phenomenon. Such exceptions, how- 

 ever, have been recognized in a greater or less degree in other 

 parts of the paleozoic column. It should be kept in mind that 

 an induction to be true must be founded on all the facts. We 

 cannot, therefore, accept as an absolute law in paleontology the 

 principle that like organic types are excluded from reappear- 

 ing in a given region after having once, and for a long time, 

 disappeared. Indeed, the doctrine of colonies proposed and ad- 

 mirably illustrated by M. Barrande, in connection with some of 

 the Bohemian rocks, is itself a striking instance of departure 

 from such a law. Nor is it easy to place a limit to the interval 

 of such possible recurrence, in the face of the fact stated by M. 

 Barrande, that in one instance a certain group of fossils makes its 

 appearance in a given stratum, then vanishes, and after the accu- 

 mulation of three thousand feet of overlying deposits, reappears to 

 form part of a great characteristic fauna. 



Such a precursory appearance of a fauna does not seem in any 

 way more probable than the repetition locally of fossil types, long 

 after the disappearance of the analogous forms which marked a 

 more ancient series of deposits. Emigration, in connection with 

 other considerations mentioned by M. Barrande, would explain 

 the one as readily as the other. 



Mr. Marcou explained the Primordial fauna of Bohemia ac- 

 cording to Barrande ; he admitted the supremacy of stratigraphy, 

 and said that precisely what he wanted in regard to disputed 

 points in the Taconic system, was a section of the country under 

 consideration ; with such a section all geologists could judge for 

 themselves, and verify or disprove the assertions in regard to it. 



Dr. C. T. Jackson exhibited a specimen of Boghead 

 coal, from Torbanehill, Scotland, containing a fine speci- 

 men of Stigmaria ; this he considers as the underground 

 stem of Slgi/lariaj and the scars of the surface as the 

 marks of buds. 



Dr. Pickering remarked that the lateral impressions on this 

 specimen looked to him like those of leaves of some coniferous 



