C. D. Walcott — The Taoonic System of Emmons. 325 



could I find a trace of the Potsdam sandstone. The sandstone 

 referred to the Potsdam is of Middle Cambrian age and, at 

 Parker's farm contains two of the same species of fossils that 

 occur in the slates conformably subjacent to the sandstone. 

 The only non-conformity found is formed by the overthrust of 

 the Georgia or Cambrian strata upon the Lower Silurian Ter- 

 rane, just as at Bald Mountain in Washington County, N. Y., 

 Snake Mountain in Vermont and all along the line of the great 

 fault, wherever outcrops of the two systems occur. 



His extension* of the "Taconic System" to include the 

 Potsdam sandstone is in opposition to all of Dr. Emmons's 

 views of the relations of the Taconic and Potsdam strata, as 

 Dr. Emmons founded the " Taconic System " largely on the 

 belief that a great stratigraphic break existed between the 

 Potsdam and Taconic, and that the fauna of the Taconic was 

 unlike that of the "Champlain group," of which the Potsdam 

 formed the base. 



Dr. Emmons's errors are nearly all traceable to his trust in 

 the lithologic characters of the various formations within the 

 Taconic area. He .established the "Taconic System" in 1842, 

 on the differences in the lithologic characters of the Taconic 

 rocks and those of the New York ' Lower Silurian.' The un- 

 conformity between the "Taconic System" and "Champlain" 

 series, announced in 1844-'4:7, was primarily based on the sim- 

 ilarity of the lithologic characters of the Calciferous sandrock 

 of the Lower Silurian and the calciferous sandrock of what we 

 now know to be, from its contained fossils, a part of his " Upper 

 Taconic" series. Again, when the latter (calciferons sandrock 

 of the Cambrian) was pushed over on to the dark shales of the 

 ' Lower Silurian,' on the line of the great fault, he identified 

 the latter shales with the " Upper Taconic " shales, and thus 

 obtained an unconformity, as at Bald Mountain, between the 

 Lower Silurian and Taconic strata. He failed to recognize the 

 fact, shown along an outcrop of a hundred miles or more, that 

 the Potsdam and, frequently, the Calciferous Terranes were 

 represented in the geologic sections by a shale undistinguishable 

 from the shale of the Hudson Terrane ; also, that the same con- 

 ditions occur in the Champlain valley, in the towns of Fort 

 Ann, Kingsbury, and Hartford, Washington County, JSf. V Y„ 

 and that, in several localities, the Trenton limestone is replaced 

 by shale. This explains much of the confusion in his stratigra- 

 phy and, also, in that of Professor Jules Marcou, in northern 

 Vermont, who was misled in the same manner. The shales 

 containing the Primordial fauna are usually lithologically dis- 

 similar from the dark argillaceous shales of the Lower Silurian, 



* Proc. Bost. Soc. Nat. Hist., vol vii, p. 371, 381, 1860. 



