381 



place between the two groups. Instead of regarding the Potsdam 

 as the first term of the Silurian rocks, I think it is the last one of 

 the Taconic system, which changes its place of bottom rocks con- 

 taining fossil remains into that of cover, capping a system of 30,000 

 feet of fossiliferous strata, containing at different levels, especially 

 the upper half, the remains of organic beings left by the Primor- 

 dial fauna. 



The Taconic system, contrary to the other members of the 

 Paleozoic series of North America, has been subjected to dislo- 

 cations on a vast scale, and presents almost always strata up- 

 heaved, broken up, and in the most disturbed state, with the 

 exception of the upper portion or Potsdam group. Generally, 

 along the Alleghany range, the Lower Silurian rocks follow imme- 

 diately ; although in Canada, Vermont, and New York, patches 

 of Hudson River group, Utica slate, Trenton limestone, Chazy 

 limestone, and Calciferous sandrocks, indicate that the Lower 

 Silurian strata have recovered in discordance of stratification 

 some parts of the country where the Taconic strata were up- 

 heaved and dislocated. In Pennsylvania, Virginia, and North 

 Carolina, New Red Sandstone covers the Taconic strata, proba- 

 bly, also, in Maine and New Brunswick. In the elevation of 

 land comprised between the Upper Mississippi, Lake Superior, 

 and Lake Michigan, the Taconic system is well developed, resting 

 on granite ; it is formed of slates, mica-schists, quartzites, lime- 

 stones, iron breccia, and is terminated by what D. D. Owen has 

 called Lower sa7idstone of the Upper Mississippi, or formation. I. 

 Until now, fossil remains have only been found in the upper part 

 of the system, on the St. Croix River, where Mr. Owen has indi- 

 cated and described Trilobites and Lingul^e, indicating the Pri- 

 mordial fauna. Fragments of Primordial Trilobites, and Lingulse, 

 have also been found near Lake Michigan, and on the Menomonee 

 and Escanaba rivers. On the southern part of the elevation of 

 land alluded to, the Taconic strata are followed and recovered by 

 the Silurian rocks, while on the northern part, that is to say, in the 

 Lake Superior direction, they are covered in discordant stratifica- 

 tion, as in North Carolina, by the Triassic strata of the Lake 

 Superior sandstone formation. Taconic strata exist also on the 

 northern shore of Lake Superior, especially near the Pic and 



