from a limestone of the original Taconic. 243 



from corresponding New York rocks. He says (p. 139), " we 

 find no fossils in the rocks of which I am speaking, and hence 

 can derive no aid from that source upon which any reliance 

 can be placed." He states no case of unconformability with 

 the New York rocks. In a later publication he refers to a case 

 of dislocation, as he terms it, in the Hoosic region, but not to 

 any of true unconformability. Dislocation, that is, faulting, it 

 is well known, proves nothing as to distinction of system; and 

 the particular facts at Hoosic referred to are proved to be of 

 merely local interest, by the general range of facts in the 

 Taconic region. 



Through the use of his lithological canon, — his, for he was 

 the first to announce it — Professor Emmons had identified, by 

 1844,* areas of Taconic rocks in Rensselaer County, New York, 

 Northern Vermont, Canada,' Maine, Rhode Island and Michi- 

 gan ; and later, in New Jersey, Virginia, North Carolina and 

 Georgia; and others have used the canon since with equal suc- 

 cess, even sometimes at very long range. 



In saying that such a use of lithological distinctions was un- 

 warranted, I mean to assert that geological investigation with 

 reference to the canon had not advanced so far as to make its 

 application safe, and render it certain that fossils might not 

 yet be discovered to upset the conclusion. I mean to assert, 

 further, that the conclusion does not now stand against actual 

 discoveries of Silurian fossils later than Potsdam that have 

 recently been made. 



The history of Taconic geology suggests caution with regard 

 to the use of lithological distinctions as evidence of geological 

 age. It shows how easy it is, under such prompting, to put 

 assumptions for facts, to say " I know " when one ought to say 

 "I doubt," and to build up systems that are likely to fall to 

 pieces. 



Professor Emmons, after he had found slates in Washington 

 County, New York, looking like Taconic, and which he called 

 Taconic, made the discovery in them of trilobites, large trilo- 

 bites, which Barrande later pronounced to be Primordial species. 

 This was evidence to him that these beds were of later age 

 than the typical Taconic, and so he made for them the subdi- 

 vision of Newer Taconic. The discovery was a grand one, and 

 may well give us a high, opinion of Prof. Emmons as a geo- 

 logical observer. But the conclusion that the rocks were rocks 

 of his Taconic system had not been proved. 

 • Prof. Emmons, in his American Geology, where he makes 

 his latest exposition of the Taconic subject (covering with it 



* Chapter on the Taconic System of his JST. T. Agricultural Eeport (1846), 

 issued in advance of the volume under date of 1844. 



f " American Geology," by Prof. E. Emmons. 1855, Part II, p. 40. 



