This mineral occurs at Keweena Point, on Lake Superior. It is found in connection with isolated blocks of amygdaloid, of primitive greenstone, and of petrosilex. Sometimes native copper, and carbonate of copper, are also present in the same specimen. In some instances, a partial decomposition has taken place, converting its green color into greenish-white, or perfect white, and rendering it so soft as to be cut with a knife. Sometimes the grains or masses of native copper are interspersed among the prehnite, and slender threads of this metal occasionally pass through the aggregated mass of greenstone, prehnite, &c., so that, on breaking it, the fragments are still held together by these metallic fibres.
8. Hornblende.
1. Common Hornblende.—Occurs as a constituent of the hornblende rocks near Point Chegoimegon, Lake Superior. Also, at the Peace Rock, on the Upper Mississippi, and in certain granite aggregates, and rolled masses of porphyries, &c., around the shores of Lakes Huron, Michigan, and Superior.
2. Actynolite.—In slender, translucent, greenish crystals, pervading rolled masses of serpentine, on the west shores of Lake Michigan.
9. Woodstone.
1. Mineralized Wood.—In bed of the River Des Plaines, Illinois.
2. Agatized Wood.—This variety of fossil wood is found along the alluvial shores of the Mississippi and of the Missouri.
c. Calcareous Minerals.
Carbonate of Lime.
Of a substance so universally distributed throughout the western country, it will not be necessary to give many localities, and these will be principally confined to its crystalline forms.
Subs. 1.—Calcareous Spar.