44G 



THE AZOIC SYSTEM AND ITS SUBDIVISIONS. 



In his Presidential Address before the American Association for the 

 Advancement of Science in 1871, Dr. Hunt said ; 



" The Taconic system as defined by him [Emmons] may be briefly de- 

 scribed as a series of imcrystalline fossiliferous sedimenta, rejjosing uncon- 

 formably on the crystalline schists of the Green Mountains, and partly mnde 

 up of their ruins ; while it is, at the same time overlaid unconformably 

 bv the Potsdam -and calciferous formations of the Champhdn, and consti- 

 tutes the true base of the paleozoic column, — thus occupying the position 



of the British Cambrian The objections made by Emmons to Bogers's 



view of the Champlain age of the Taconic rocks were threefold : first, 

 the great differences in lithological characters, succession, and thickness, 

 between these and the rocks of the Champlain division . . . . ; second, the 

 supposed unconformable infraposition of a fossiliferous series to the Pots- 

 dam ; and third, the distinct fauna which the Taconic rocks were supposed 

 to contain. The first of these is met by the fact now established that in 

 the Appalachian region the Champlain division is represented by rocks hav- 

 ing, with the same organic remains, very different lithological characters, and 

 a thickness tenibld greater than in the typical Champlain region of Northern 

 New York. The second oljjection has already been answered by showing that 

 the rocks which, as in the St. Albans section, pass beneath the Potsdam, are 

 really newer strata belonging to the upper part of the division, and contain a 

 characteristic fossil of the Utica slate. As to the third point, it has also been 

 met, so far as regards the Atops and EUiptoceplialus, by showing these two 

 genera to belong to the Potsdam formation. If we inquire further into the 

 Taconic fauna, we find that the Stockbridge limestone (the Eolian limestone 

 of Hitchcock), which was placed by Emuions near the base of the lower Ta- 

 confc (while the Olenellus slates are near the summit of the Upper Taconic), is 

 also fossiliferous, and contains, according to the determinations of Prof. Hall, 

 species belonging to the genera Euomphalus, Zaphrentis, Stromatopora, Chae- 

 tetes, and Stictopora. Such a fauna would lead to the conclusion that these 

 limestones, instead of being older, were really newer tlum the Olenellus beds, 

 and that the apparent order of succession was, contrary to the supposition of 

 Emmons, the true one. This conclusion was still further confirmed by the 

 evidence obtained in 18G8 by Mr. Billings, who found in that region a great 

 number of characteristic species of the Levis formation, many of them in beds 

 immediately above or below the white marbles, which latter, from the recent 

 observations of the Bev. Augustus Wing, in the vicinity of Rutland, Vermont, 

 would seem to be among the u])per beds of the Potsdam formation. Thus 

 while some of the Taconic fossils belong to the Potsdam and Utica formations, 

 the greater number of them, derived from beds supposed to be low down in the 

 system, are shown to be of the age of the Levis formation. There is, there- 

 fore, at present, no evidence of the existence, among the unaltered sedimentary 

 rocks of the western base of the Appalachians in Canada or New England, of 

 any strata more ancient than those of the Champlain division, to which, from 



