TACONIC QUESTION IN GEOLOGY. 129 



east ; in the first locality resting nnconformably upon Ordovician strata, and in the second, 

 upon a mass of eruptive rock which breaks through similar strata (§ IIT). In this connec- 

 tion may be recalled the like occurrence at Becraft's Mountain, near the town of Hudson, 

 on the east side of the Hudson River, long known, and lately re-examined by "W. M. 

 Davis. Here, resting upon shales referred to the Hudson River group and, from the 

 locality, probably of Loraine age, there is found, in a small synclinal area, a mass of con- 

 torted strata, including 150 feet or more of fossiliferous Lower Helderberg limestones over- 

 laid by as great a thickness of Cauda-galli shales, to which succeed a few feet of 

 cherty limestone regarded as the equivalent of the Corniferous or Upper Helderberg. ' In 

 all of these localities, as well as at Eondout, also reexamined by Davis, we note the 

 absence, beneath these Silurian strata, of the great mass of mechanical sediments, including 

 the Oneida and Medina sandstones, which, farther west, are so conspicuous in the lower 

 part of the Silurian series, and belong to the Second Graywacke of Eaton. 



§ 148. As already mentioned in § 118, Augustus Wing, having detected in Yermont 

 fossiliferous limestones of Trenton age, the locality was examined by Billings. In a section 

 eastward from Crown Point, in New York, the latter found what was described as the 

 Red Sand-rock, with Olenellus, brought up by a fault, on the east side of the Loraine 

 shales, and followed eastward by strata carrying the fauna of the Calciferous sand-rock, 

 succeeded by some forms of the Levis, and then by the Chazy and Trenton ; to the east of 

 which another dislocation brings up again a limestone abounding in the typical fauna of 

 the Levis limestone. The close association of the latter with the white marbles quar- 

 ried in this region, led Billings to refer these to the Levis horizon.^ It is worthy of notice 

 that it was in ihe same vicinity, which furnished Billings with Calciferous, Levis, Chazy 

 and Ti-enton forms, that the organic remains had been found which were referred by Hall 

 to the Niagara and still higher horizons, and which led Edward Hitchcock and "W. B. 

 Rogers to conjecture that the marbles of this region might be of Devonian age or younger. 

 So perplexing were these facts to "Wing, that we find him led to the conclusion, announced 

 in a letter to J. D. Dana in 18Y5, and recently cited with approval by the latter,'^ that 

 " The Eolian limestone of the Yermont G-eological Report embraced not only the Trenton 

 and the Hudson River beds, but all the formations of the Lower Silurian as well, and even 

 limestones and dolomites of the Red Sand-rock (Potsdam sandstone) series." 



§ 149. Another hypothesis touching the age of the Taconic marbles was now ofiered 

 to the ]5erplexed geologist, and this time by the G-eological Survey of Canada. We have 

 already shown that forced by the paleontological evidence (which had previously been 

 urged by Emmons), Logan, in 1860, adopted the views of the latter as regards the horizon 

 of the Upper Taconic, long before traced from New York to below Quebec on the St. Law- 

 rence. This, in accordance with the conclusions of Mather, and the earlier published view 

 of Emmons, had been described by Logan as consisting of the Hudson River group with 



' Amer. Jour. Science, xsvi, 381 and 389. 



* Hunt, On Some Points in the Geology of Vermont, 1868, Amer. Jour. Science, xlvi, pp. 222, 229. Tliis paper, 

 from data furnislied by Billings, was written while the writer still accepted the untenable view of Logan, from the 

 first opposed by Billings, which assigned the Levis to a position near the base of the Cambrian series, instead of 

 its summit. 



^ Dana, The Age of the Taconic System, Quar. Geol. Jour., xxxviii, 402. 



Sec. IV., 1884. 17. 



