350 APPENDIX. 



7. Pkehnite. 



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 cop- 

 per, and carbonate of copper, are also present in the same speci- 

 men. 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 Hornhlende. — Occurs as a constituent of the horn- 

 blende rocks near Point Chegoimegon, Lake Superior. Also, at 

 the Peace Eock, 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, per- 

 vading 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. 



1. 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 j)rincipally confined to its crystalline forms. 



Subs. 1. — Calcareous Spar. 



Crystallized Calcareous Spar. — This mineral occurs, in minute 

 rhomboidal crystals, in the calcareous rock of the Island of 



