C. D. Walcott — The Taconic System of Emmons. 319 



Another illustration of the supposed overlap of the Cham- 

 plain upon the Taconic Terrane is given in the American 

 Geology, pt. 2, p. 72, fig. 12. It is in the township of Green- 

 bush, opposite Albany, 1ST. Y , on Cantonment Hill. There 

 a mass of the Trenton limestone is caught on the line of the 

 great fault separating the Champlain and Cambrian strata, as 

 at Bald Mountain and other places in Washington county, and, 

 also, in Yermont. The strata of the Hudson and Trenton 

 Terranes are broken and displaced, but there is no evidence 

 that the Trenton was deposited upon the upturned edges of the 

 Cambrian or " Upper Taconic " slate ; and, on the line of the 

 same fault, 20 miles to the south, in the township of Schodack, 

 Mr. S. "W. Ford discovered an unconformable contact between 

 the dark drab siliceous and micaceous shales of the Cambrian and 

 the dark argillaceous shales of the Hudson Terrane.* Mr. Ford 

 kindly took me to the locality which he has so well described, 

 and I saw the " hade " of the fault, the slickensides on the op- 

 posing surfaces, and broke out graptolites from the Hudson 

 shales beneath, and within six inches of, the fault line. A 

 short distance south the limestones interbedded in the dark- 

 drab shales gave us an abundance of characteristic Middle Cam- 

 brian fossils. For the details of this overthrust of the Cam- 

 brian upon the Hudson Terrane, see Mr. Ford's paper. 



Dr. Emmons illustrates another sectionf that shows the same 

 errors of observation as in the figure of the section at Can- 

 tonment Hill. Again, in fig. 224 of the section at Snake 

 Mountain, in Yermont, the error made at Bald Mountain is 

 repeated, for it is now well known that the supposed overlying 

 Calcif erous (?) sandrock (" B,ed sandrock ") is a stratum of the 

 Cambrian pushed over on to the Lower Silurian Terrane,§ 

 and not a Lower Silurian formation, unconformably superja- 

 cent to the " Upper Taconic " strata. 



All the overlying limestones that he mentions as unconform- 

 ably overlying the Taconic rocks, with the exceptions noted, 

 where they contain Middle Cambrian fossils, are west of the 



rane. off shore, was originally deposited either as a calcareous or argillaceous rnud. 

 It was owing to this oversight that he frequently identified the shales of the 

 Champlain series as those of the Taconic. Another phenomena not understood 

 by him, was the creeping or protruding of shales from beneath heavy masses of 

 limestone, on account of the pressure squeezing the shales out and turning them 

 up. In this way many of his non-conformities of dip appear to have been erro- 

 neously observed. In many instances he did not recognize the lithologic differ- 

 ences between the great mass of his Taconic slate and that of the Hudson Terrane. 

 The black shale (marked "Taconic," in the Bald Mountain section, b, V, rig. 11) 

 is not similar to the shale containing the trilobites, east of the great fault, yet he 

 identified them as lithologically the same formation. 



* This Journal, vol. xxix, p. 16, 1885. 



f Am. Geol., voL i, pt. 2, p. 79, fig. 14, 1856. 



% Loc. cit., p. 87. 



§ This Journal, III, vol. xiii, p. 413, 1877. 



