on the Taconic System. Ill 



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 Geological 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 dislocations ; 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 con- 

 stituting the typical group of Hudson River. This is verified by 

 the note of Mr. Hall, for he tells us that Sir W. E. Logan is in- 

 clined 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, at first view, to 

 have been but doubtfully determined, and in complete opposition 

 to palseontological documents. 



*' I do not think, then, that I weaken in the least degree the 

 respect and confidence justly inspired by the labors of the Ameri- 

 can 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 impor- 

 tant question. 



** Doubtless, thanks of the progress of our knowledge, we are 

 now no longer bound by the ancient conception of the simultane- 

 ous extinction and the total renovation of the faunae. As for my- 

 self, in particular, it would not be possible to accuse me of similar 

 views at the moment when I am publishing the explanation of my 

 doctrine of colonies. But you will perceive 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 faunas the second fauna occupies the 

 greatest vertical space and is probably the one which enjoyed the 

 longest existence. Thus, to verify such a reappearance, the most 

 incontestable proofs are required, for such a decision would com* 

 pel the entire re-formation of one of our most important scientific 

 creeds. « Yoursj very truly, 



J. BARRANDE." 



