XIII.] GEOGNOSY OF THE APPALACHIANS. 265 







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 Ellipto- 

 cephalus, by showing these two genera to belong to the Pots- 

 dam formation. If we inquire further into the Taconic fauna, 

 we find that the Stockbridge limestone (the Eolian limestone 

 of Hitchcock), which was placed by Emmons near the base of 

 the Lower Taconic (while the Olenellus slates are near the sum- 

 mit of the Upper Taconic), is also fossiliferous, and contains, 

 according to the determinations 'of Professor Hall, species be- 

 longing to the genera Euomphalus, Zaphrentis, Stromatopora, 

 Chaetetes, and Stictopora.* Such a fauna would lead to the 

 conclusion that these limestones, instead of being older, were 

 really newer than the Olenellus beds, and that the apparent 

 order of succession was, contrary to the supposition of Em- 

 mons, the true one. This conclusion was still further confirmed 

 by the evidence obtained in 1868 by Mr. Billings, who found 

 in that region a great n'umber of characteristic species of the 

 Levis formation, many of them in beds immediately above or 

 below the white marbles, t which latter, from the recent obser- 

 vations of the Eev. Augustus Wing, in the vicinity of Eutland, 

 Vermont, would seem to be among the upper beds of the Pots- 

 dam 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 sys- 

 tem, are shown to be of the age of the Levis formation. There 

 is, therefore, at present, no evidence of the existence, among 

 the unaltered sedimentary rocks of the western base of the 

 Appalachians in Canada or !N~ew England, of any strata more 

 ancient than those of the Champlain division, J to which, from 



* Geology of Vermont, 419 ; and American Journal of Science (2), XXXIII. 

 419. 



+ American Journal of Science (2), XLVI. 227. 



See, on this point and on the possibly greater antiquity of the rocks 

 called Potsdam, Essay XV., Part Third. 

 12 



