TA CONIC SYSTEM. 25 



aloDg the south shore of the lake for more than forty miles, then forming 

 a narrow belt stretch in a north-east direction for about a hundred miles to the 

 extremity of Keweenaw Point. The copper occurs in a rock called melaphyre, 

 associated with beds of conglomerate, and appears to be interstratified with them. 

 Sometimes bands of slate separate beds of melaphyre. The native copper exists in 

 sheets, strings, and masses, and is sometimes associated with silver. In Ashland 

 County, Wisconsin, the copper-bearing series has a thickness of more than four miles, 

 though not very rich in the ore. The Taconic area in Minnesota is large. It 

 extends across the northern border, and forming an elbow in the north-east extends 

 diagonally through the State to the south-west corner. Here there is a hard, red- 

 dish, metamorphic sandstone, called the Sioux quartzite, interstratified with which 

 is a layer of red indurated clay or pipestone, one foot thick, called Catlinite, 

 largely used for the manufacture of pipes. The quarry is thirty miles north of 

 the south-west corner of the State, and four miles east of the west line. The Sioux 

 quartzite occurs in the north-west corner of Iowa. 



§ 45. The geographical extent of these rocks in Canada is very great. They 

 may be traced from near Lake Temiscaming 80 miles north-west of Lake Nipissing, 

 south-westward to Lake Huron, and from thence westward on the north shore of the 

 lake and the north shore of Lake Superior, and on beyond Lake of the Woods, a 

 distance in all of about 800 miles. They pass beneath the lakes and expose a large 

 area in the Upper Peninsula of Michigan at Marquette and Menominee, and a great 

 thickness, extending from the lowest to the highest Taconic, as first ascertained by 

 Houghton; thence they pass into Wisconsin, exposing a large area and quite as 

 complete a representation of the series, while another arm extends from Duluth into 

 Minnesota. The thickness in Michigan is about four miles; but in Wisconsin, 

 including the copper-bearing series, which is three-fourths of igneous material, the 

 thickness is much greater; and even excluding the igneous material the thickness 

 exceeds four miles. The upper part of the Taconic System in Wisconsin, formerly 

 called the " Copper-bearing series," has received the unattractive name of the 

 Keweenawan formation, from the Keweenaw Point; but as it is part of the Taconic 

 System the preferable name is the older one of the "Copper-bearing series." The 

 rocks appear between Scoresby Bay and Cape Cresswell, in Lat. 82° 40' N., where 

 Nares and Feilden called them Cape Kawson beds. 



§ 46. In 1856 Emmons divided the System into Upper and Lower Taconic. 

 The Canadian Geologists in 1863 placed his Upper Taconic in the Silurian System 

 and called it "Lower Potsdam," which name therefore became a synonym. The 

 only geographical names which have been used to subdivide the Upper Taconic into 

 Groups, which seem in the present state of learning to be worthy of retention, are, 

 in descending order, the Swan ton Group, the Georgia Group, and the St. John 

 Group — if in fact the latter is below the Georgia, and therefore not a synonym. 

 Emmons placed the Stockbridge limestone in the Lower Taconic; but it would seem 

 from the examinations made by others, that his division would have been more 

 clearly marked if the Stockbridge limestone had been retained in the Upper Taconic. 

 The Paradoxides beds at Braintree, Mass., in Newfoundland and New Brunswick, 

 and wherever found on the continent, belong to the Upper Taconic. The same diffi- 

 culty exists in the West, in separating the Upper Taconic from the overlying rocks of 

 the Potsdam, that has led to so much discussion in the East; and the confusion is 



