Account of the Native Copper on Lake Superior. 349 
reserving as the subject of a future communication, the facts I 
have collected on the mineralogy of the country explored gene- 
rally. 
The first striking change in the mineral aspect of the country 
north of Lake Huron, is presented near the head of the island of 
St. Joseph in the river St. Mary, where the calcareous strata of 
secondary rocks are succeeded by a formation of red sand-stone, 
which. extends northward to the head of that river at Point Iro- 
quois, producing the fails called the Sault de St. Marie fifteen 
miles below, and thence stretching northwest along the whole 
soutiiern shore of Lake Superior to the Fond du Lac, and into 
the regions beyond. This extensive stratum is perforated at 
various points by up-heaved masses of granite and hornblende, 
which appear in elevated banks on the margin of the lake be- 
tween Dead river and Presque Isle, and from the Porcupine 
mountains ten leagues to the west of the Ontonagon river. It is 
overlayed in other parts by a stratum of grey sand-stone, resem- 
bling certain varieties of grauwacke, of uncommon thickness, 
which appears in various promontories along the shore, and, t 
the aistance of ninety miles from Point Iroquois, constitutes a 
lofty perpendicular wall upon the water’s edge called the Pictured 
Rocks, which is one of the most commanding objects in nature. 
So obvious a change in the geological character of the rock strata, 
in passing from Lake Huron to Lake Superior, prepares us to 
expect a corresponding one in the imbedded minerals and other 
natural associations,—an expectation which is realized during 
the first eighty leagues, in the discovery of red hematite, prehnite, 
opal, jasper, sardonyx, carnelion, agate, and zeolite. 
The first appearances of copper are seen on the head of the 
portave across Keweena point, two hundred and seventy miles 
beyond the Sault de St. Marie, where the pebbles along the shore 
of the lake contain native copper disseminated in particles vary- 
ing in size from a grain of sand to a lump of two pounds weight. 
Many of the detached stones at this place are also coloured green 
by the carbonate of copper, and the rock strata in the vicinity 
exhibit traces of the same ore. ‘These indications continue to 
the river Ontonagon, which has long been noted for the large 
masses of native copper found upon its banks, and about the con- 
tiguous country. This river (called Donagon on Mellish’s Map) 
is one of the largest of thirty tributaries’ which flow into the 
lake between Point Iroquois and the Fond du Lac. It originates 
in a district of mountainous country intermediate between the 
Mississippi river and the Lakes Huron and Superior, and, after 
running in a northern direction for one hundred and twenty 
miles, enters the latter at the distance of fifty-one miles west 
of Point Keweena, in north latitude 46° 52’ 2” according 
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