OF THE N 0 11 T II W E S T. 



53 



b 1 



' Second Trilobite 

 bed. 



First Trilobite 

 bed. 



Coarse lingula grit, green, yellow, sometimes almost white, 



Fine grit. Place of the Menominie Trilobite grit.(?) White 

 and yellow sandstone, and Obolus layers of Black River, 



Ferruginous Trilobite grits. Schistose sandstone, containing 

 fork-tailed Trilobite beds, and Obolus layers, . 



Matmesio-calcareous rock, with Obolus and fork-tailed Trilobite 



Highly fossiliferous, schistose, siliceo-calcareous layers, inter 

 laminated with argillaceous, marly beds, charged with sul 

 phate of iron ; the former full of Lingulas and Orbiculas 

 (Falls of St. Croix), 



Feet. 

 100 to 180 



15 



1 to 8 



3 



50 



Sandstone, with oblique lines of deposition, alternating with 

 pebbly sandstones, and coarse grits of the Chippewa, and 

 Black, and Wisconsin Rivers, near the Falls, . . . 50 to 100 



Place of the Lake Superior ferruginous and argillaceous sand- 

 stones, shales, and conglomerates, ..... 5,000 



SECTION III. 



ITS MINERAL CONTENTS. 



The series composing F. 1, which we have now under consideration, consists, 

 therefore, chiefly of light-coloured, quartzose, soft sandstone, with some intercala- 

 tions of argillaceous, argillo-calcareous, and earthy, deposits. Such incoherent 

 beds are unfavourable for the retention of mineral matters, since they present to 

 any rents, fissures, or horizontal openings which may traverse them, crumbling and 

 unstable walls, and, consequently, do not retain that openness of fissure favourable 

 for the reception of ores and the accompanying spars. We have seen, however, 

 that there are intercalations of magnesian limestone interposed between these 

 strata. These are more favourable for the retention of metallic veins ; but they 

 form, at most localities, only a subordinate part of the whole. 



J udging from the experience of other mining districts, the country over which 

 these rocks prevail is not likely to be a productive mineral region ; nevertheless, 

 between the Mississippi and Kickapoo, on the southeast quarter of Section 27, 

 Township 10 north, Range 5 west, of the 4th Principal Meridian, where the 

 formation in question forms the basis of the adjacent country, copper ore has been 

 discovered ; not, however, in immediate connexion with the sandstone. For the 

 wall-rock to which the ore was traced, and which bounds it on the southeast, is a 

 true magnesian limestone, possessing the characters usual in that formation through- 

 out the lead and copper localities of the Mineral Point District, yet belonging to an 

 older subdivision of the Protozoic rocks. 



This Kickapoo copper ore is of rather a singular character ; it is of a light green 

 colour, with a waxy lustre and fracture, and very brittle. It is disseminated 



