374 



testimony to guarantee the exactness of the position of a few fossils, it 

 is clear that the determination of this position is difficult. 



" In order to understand these difficulties I have consulted the maps 

 and documents relating to the State of Vermont and the country in which 

 the town of Georgia is situated, and, although the library of our Geo- 

 logical Society does not contain all that one could wish on this subject, 

 I recognized easily that Georgia is placed in the region where the order 

 of succession of the deposits is the most obscured by foldings and dislo- 

 cations ; so that the position of the schists in question could not have 

 been determined by the incontestable evidence of direct superposition. 

 Besides, the physical appearance of these schists is not that of the rocks 

 constituting the typical group of Hudson River. This is verified 

 by the Note of J. Hall, for it tells us that Sir W. E. Logan is inclined 

 to make a distinct group of these schists superior to that of the Hudson, 

 and which consequently would crown the whole Lower Silurian division of 

 the continent. 



" For the above reasons, the geological horizon on which the three 

 Oleni of Georgia were found appears to me to have been but uncer- 

 tainly determined at first view, and even in complete opposition to 

 paleontological documents. 



" I do not think, then, that I weaken in the least degree the respect 

 and confidence justly inspired by the labors of the American savants 

 whose names have just been mentioned, when I ask them in the name 

 of science to make new researches and new studies, that may lead to a 

 final and certain solution of this important question. 



" Doubtless, thanks to the progress of our knowledge, we are now no 

 longer bound by the ancient conception of the simultaneous extinction 

 and the total renovation of the faunae. For myself, in particular, it 

 would not be possible to accuse me of similar views at the moment when 

 I pubhsh the explanation of my doctrine of colonies. But you will j)er- 

 ceive that the facts which I invoke in support of this doctrine are far 

 from sustaining the reappearance of a fauna after the extinction of the 

 following fauna, which the three trilobites of Georgia would do, if they 

 had really lived after the deposit of the Hudson River group. 



" This reappearance would be still more astonishing, as among the 

 three great Silurian faunae the second fauna occupies the greatest ver- 

 tical space and is probably the one which enjoyed the longest existence. 

 Thus, to verify such a reapj)earance, the most incontestable proofs are 

 required, for such a decision would oblige the entire re-formation of one 

 of our most important scientific creeds. 



" Yours very truly, 



"J. BARRANDE." 



