33-i APPENDIX. 



pursued in caves, or, more properly, fissures in the rock. In one 

 of the excavations which I visited, the digging was continued 

 horizontally under the first stratum of rock, after an excavation 

 had been made perpendicularly, through the top soil and calca- 

 reous rock, perhaps thirty feet. The ore is a broad-grained cu- 

 bical galena, easily reduced, and bids fair very greatly to enhance 

 the value and resources of this section of the West. 



Similar mines exist at Mississinawa, and the Eiver Au Feve,* 

 both on the eastern or left bank of the Mississippi, And a sys- 

 tem of leasing or management, such as I have suggested for the 

 Missouri mines, appears equally desirable. 



Quartz Geodes. — The amount of silex in the cliff limestone is 

 such, in some conditions of it, as to justify the term silico-calca- 

 reous. This condition of the rock at the passage of the Missis- 

 sippi through the Eock River and Des Moines Rapids, is such as 

 to produce a very striking locality of highly crystalline quartz 

 geodes, which accumulates in the bed of the stream. Many of 

 these geodes are from a foot to twenty-two inches in diameter, 

 and on breaking them they exhibit resplendent crystals of limpid 

 quartz. Sometimes these are amethystine; in other cases they 

 present surfaces of chalcedony or cacholong. The latter minerals, 

 if obtained from the rock, and before unduly hardening by ex- 

 posure, would probably furnish a suitable basis for lapidaries. 



Intermediate Country in the Direction to Green Bat. — 

 There is a line which separates, on the north, the granitical and 

 trap region from the metal-bearing limestone, and its supporting 

 sandstone. This formation of the elder series of rocks, having 

 been traced to the south shore of Lake Superior, and having 

 been seen to constitute the supporting bed of the alluviums and 

 diluviums of the Upper Mississippi, above the Peace Rock, it 

 may subserve the purpose of inquiry to trace this line of junction 

 by its probable and observed boundaries. 



The line may be commenced where it crosses the Mississippi, 

 at the Peace Rock, and extended to the St. Croix, the falls of 

 which are on the trap-rock, to the sources of the Chippewa at 

 Lac du Flambeau, and the Wisconsin near Plover Portage. The 

 source of Fox River runs amid uprising masses of sienite, and 

 this formation appears to pass thence northeasterly, across the 



* Galena has subsequently been made the capital of these mines. 



