283 



CHAP. XXXVIII. 



THE SILURIAN AND DEVONIAN SERIES. 



Kim of the Silurian Series. — Distribution of Formations. — The Chazy 

 Formation. — Fossils from the Chazy, Modiplopsis Parviuscula, Ortho- 

 ceras Sim])soni. — Bird's-eye, and Trenton Formations. — Hudson River 

 Formation. — The Devonian Series. — Salt Springs. — Salt Springs in 

 Rupert's Land. — Manufacture of Salt. — Salt Trade of the United States. 

 — Fossils from Devonian Rocks in the Winnipeg Basin. 



THE SILURIAN SERIES. 



The rim of the great southern fossiliferous basin in North 

 America touches Fond du Lac, the western extremity of 

 Lake Superior.* From this point it makes a bend to the 

 south, and then turning north-westerly comes upon the 

 Mississippi river near its source. The prolongation of the 

 great granitic axis separating the waters flowing into Lake 

 Superior, from those tributary to Lake Winnipeg, pene- 

 trates for a considerable distance into the fossiliferous basin, 

 in the northern part of the State of Minnesota, but although 

 the subjacent rock is concealed by drift, the general charac- 

 ter of the country, as far as Eed Lake, leads to the in- 

 ference that it is underlaid by the Silurian series. From 

 Eed Lake the rim pursues a northerly course to the 

 mouth of Eainy Eiver ; it underlies the valley of Eainy 

 Eiver, as far as Eainy Lake, in the form of a narrow and 



* Sandstones belonging to the Potsdam and Chazy formations, the lowest 

 members of the fossiliferous rocks in America, are in great force on the 

 south shore of Lake Superior. The basin of the lake is chiefly excavated 

 in the Potsdam sandstone. 



