OF THE NORTHWEST. 53 
Feet. 
c Coarse lingula grit, green, yellow, sometimes almost white, 100 to 130 
‘Second Trilobite § Fine grit. Place of the Menominie Trilobite grit.(?) White 
bed. and yellow sandstone, and Obolus layers of Black River, . 15 
. +) ys Ferruginous Trilobite grits. Schistose sandstone, containing 
nae erry fork-tailed Trilobite beds, and Obolus layers, . 1to8 
bs ; Magnesio-calcareous rock, with Obolus and fork-tailed Trilobite, 3 
Highly fossiliferous, schistose, siliceo-caleareous layers, inter- 
laminated with argillaceous, marly beds, charged with sul- 
phate of iron; the former full of Ling — and Orbiculas. 
(Falls of St. Croix), F 50 
Sandstone, with oblique lines of deposition, alternating with 
pebbly sandstones, and coarse grits of the Chippewa, and 
a Black, and Wisconsin Rivers, near the Falls, . : . 50 to 100 
Place of the Lake Superior ferruginous and argillaceous sak 
stones, shales, and conglomerates, . : : : é 5,000 
SECTION III. 
ITS MINERAL CONTENTS. 
Tue series composing F. 1, which we have now under consideration, consists, 
therefore, chiefly of lighteoloureds quartzose, soft sandstone, with some intercala- 
tions of argillaceous, argillo-caleareous, 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. 
Judging 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 
