326 G. D. Walcott — The Taconic System of Emmons. 



but, as Dr. Emmons included the dark graptolitic-bearing shales 

 of the Hudson Terrane, within the Taconic area, in the "Upper 

 Taconic," he necessarily compared and identified the black 

 shales of the Lower Silurian with the " Black Slate " of the 

 " Upper Taconic." He could scarcely do otherwise, when the 

 stratigraphy along the western side of the " Taconic System " 

 supported his theory, if such an identification of the shale was 

 made. 



The fact that the Potsdam sandstone, as a lithologic forma- 

 tion, is a local deposit in the immediate vicinity of the Adiron- 

 dack mountains and that the sediments being deposited at the 

 other localities at the same time, embedding similar organic 

 remains, were argillaceous, siliceous and calcareous muds, does 

 not seem to have impressed him, although he devotes many 

 pages of his various memoirs to the description and discussion 

 of the lithology of the Taconic and Lower Silurian rocks. 



Dr. Emmons was not a collector of fossils, or he would have , 

 found them in nearly all the formations within the Taconic 

 area ; and I think that no student conversant with the faunas 

 of the Lower Silurian and Cambrian terranes will long hesitate 

 in concluding that he did not have sufficient critical knowledge 

 of the faunas to which the fossils belonged that he did obtain, to 

 identify the strata from which they came on paleontologic 

 evidence otherwise he could not have so confused them.* 

 When Dr. Fitch gave him the fossils that he had found in the 

 " Black Slate," two miles north of Bald Mountain, in 1843, he 

 at once referred them to a pre-Potsdam horizon, on stratigraphic 

 evidence, without making any comparisons with a fauna which 

 he knew to be pre-Potsdam at some other locality. In fact, no 

 such data were at his command at that time, and the reference 

 of the fossils to a pre-Potsdam horizon was based entirely upon 

 the fact that they were in strata which he considered to be situ- 

 ated unconformably beneath the Potsdam sandstone or, in its 

 absence, the Calciferous sandrock. 



1 wish to mention here that, in 1847, Dr. Emmons did 

 not consider the two species of trilobites as characteristic of the 

 true Taconic slate, but of the overlying " Black Slate," which 

 he considered to be pre-Potsdam, from the evidence of the 

 Bald Mountain section. I also call attention, again, to the fact 

 that there was no valid stratigraphic evidence of the pre-Pots- 

 dam age of the " Black Slate ;" moreover, as I have shown, the 

 "Black Slate" is the lowest member of the "Taconic System" 

 and not the highest, as stated by him, in 1847, or next above 



* It is not practicable for me, owing to want of space, to give a full analysis of 

 the paleontologic work done by Dr. Emmons in connection with his argument for 

 the Taconic system. This will appear in my report on the geology of Washington 

 County, N. Y. 



