In large isolated masses in the bed of the Illinois River, on the shallow rapids between the junction of the Fox and Vermilion Rivers. It is mostly arranged in stripes or circles of white, gray, yellow, &c., resembling certain jaspers, or approaching sometimes to hornstone. The bed of the Illinois River, at this place, is a species of gray sandstone. Also, in detached fragments, on the south shore of Lake Superior, intimately mixed with prehnite. In regard to the latter, Professor Dewey, of Williamstown College, writes me: "I have received from Dr. Torrey, a curious mixture of petrosilex and prehnite, in imperfect radiating crystals, which was sent him by you and collected at the West. He did not tell me the name, but examination showed what it was. The association is singularly curious." The locality of this mineral is Keweena Point, Lake Superior.
4. Mica.
Occurs rarely in the granite of Lake Superior. It is found in place on the Huron Islands. Also, in minute folia, in the alluvial soil of the Upper Mississippi. A beautiful aggregate, consisting of plates of gold-yellow mica, connected with very black and shining crystals of schorl, has been dug up from the alluvial soil of the Island of Michilimackinac.
5. Schorl.
1. Common Schorl.—In crystals, in boulders of granite, at Green Bay.
2. Tourmaline.—With the preceding.
6. Feldspar.
As an ingredient in the granite of Huron Islands, Lake Superior. Also, in detached masses of granite along the west shores of Lake Michigan. Also, in the form of prismatic crystals of a light-green color, in the rolled masses of hornblende, porphyry, greenstone, and epidotic boulders of Lakes Huron, Michigan, and Superior.
7. Prehnite.