110 Barrande, Logan and Hall 



the same plan and producing an infinite variety of forms almost 

 incomprehensible to us, has never repeated the same forms in 

 successive creations. The various organisms called into existence 

 have performed their parts in the economy of creation, have lived 

 their period and perished. This we find to be as true among the 

 simple and less conspicuous forms of the palaeozoic series, as in 

 the more remarkable fauna of later periods.' — J. Sail, * Fal. of 

 New YorhJ i. p. xxiii." 



" When an eminent man expresses such ideas so eloquently, it 

 is because they rise from his deepest convictions. It must then 

 be conceived that Mr. Hall, restrained by the artificial combinations 

 of stratigraphy previously adopted by him, has done violence to 

 his palaeontological doctrines, when, seeing before him the most 

 characteristic forms of the Primordial fauna^ and giving them 

 names the most significant of this first creation, he thinks it his 

 duty to teach us that these three trilobites belong to a horizon 

 superior to that on which the second fauna is extinguished. 



** In effect, according to the text of Mr. Hall, the three trilobites 

 in question were found near the town of Georgia, Vermont, in 

 schists which are superior to the true Hudson River group. In 

 his works Mr. Hall does not go beyond indicating the horizon of 

 certain fossils, and no one would think of asking from him a guar- 

 anty for such indications. But on this occasion the great American 

 palaeontologist thinks it necessary to support his stratigraphical de- 

 termination by another authority, chosen from the most respecta- 

 ble names in geology. The following is the note which terminates 

 his Memoir. 



" ' Note. — In addition to the evidence heretofore possessed 

 regarding the position of the shales containing the Trilobites, I 

 have the testimony of Sir W. E. Logan, that the shales of this 

 locality are in the upper part of the Hudson River group^ or form- 

 ing a part of a series of strata which he is inclined to rank as a 

 distinct group, above the Hudson River proper. It would be quite 

 superfluous for me to add one word in support of the opinion of 

 the most able stratigraphical geologist of the American continent.' 



" Now, when a savant hke Mr. Hall thinks himself obliged to 

 invoke testimony to guarantee the exactness of the position of 

 certain fossils, it is clear that the determination of this position 

 presents some difficulties. 



*'In order to understand these difficulties I have consulted the 



