Miller on the laconic. 239 
7. Red quartzjte etc 2300 feet. 
8. Red jasper conglomerates etc 2150 " 
9. White quartzjte etc 2970 " 
10. Yellowish chert, etc 400 " 
11. White Quartzjte etc 1500 " 
12. Yellowish chert etc 200 " 
13. White quartzjte 400 " 
Total 18000 feet. 
Another section adds to this one 4000 feet, and even then the 
maximum thickness of the series in that locality has not been 
reached. 
Throughout the Huronian region, the whole series bears evi- 
dence of great disturbance and is frequently cut with intrusive 
masses of greenstone, granite, or other igneous rocks. The 
more recent disturbances frequently bear metalliferous veins, 
which give to the country its value as a mineral region. Cop- 
per and iron ai^e the chief minerals and abound in nearly every 
section, — gold and silver sometimes occur. The Taconic of 
Michigan contains vast beds of iron ore. The ores are mag- 
netic, red specular hematite, and soft hematite resembling the 
the brown hematite of other states. The magnetic and specul- 
ar ores are the most prized, and usually contain from 60 to 70 
per cent of ii^on and hardly a trace of phosphorus or sul- 
phur. The lake .Superior region is the chief locality of the 
world for native copper. It is so pure the aborigines manu- 
factured it into implements. The copper-bearing rocks extend 
eastward along the south shore of the lake for more than forty 
miles, then forming a narrow belt stretch in a north-east direc- 
tion, for about 100 miles, to the extremity of Keweenaw point. 
The copper occurs in a rock called melaphyr associated with 
beds of conglomerate which appear to be interstratified with 
it. Sometimes bands of slate separate beds of melaphyr. The 
native copper exists in sheets, strings and masses, and is some- 
times associated with silver. In Ashland county, Wisconsin, 
the copper-bearing series has a thickness of more than four 
miles though not very rich, in ore. The Taconic area in Min- 
nesota is large. It extends across the northern border, and form- 
ing an elbow in the northeast extends diagonally through the 
state to the southwest corner. Here there is a reddish metamor- 
phic sandstone called the Sioux quartzyte, interstratified with 
which is a layer of red indurated clav or pipestone one foot 
