56 Wiscojisin and Missouri Lead Region. 



iron, being found at the point of contact, I am led to the opinion 

 that the granite is the more recent rock, and that more veins may 

 with confidence be looked for along and near its line of junction 

 with the limestone. 



Not only do sandstone beds alternate with the limestone, but 

 in the vicinity of known lead mines, particularly, the limestone 

 comprises heavy beds of a cavernous, siliceous rock, exceedingly 

 hard, like the French burrstone, and like it sometimes suitable for 

 millstones. There too abound in it mam miliary and botryoidal 

 masses of quartz rock coated with crystals, veins of calcareous 

 spar, known by the name of " iif,^^ and lumps and beds of he- 

 matite iron ore, all which are now considered in Missouri indica- 

 tive of the proximity of lead ore veins. These, unlike the copper 

 ore veins noticed, occur at a distance from the granite, which 

 agrees well with the position of lead and copper mines in Corn- 

 wall ; tin and copper being there found near granite, and lead, 

 antimony, manganese, iron, &c. at a distance from it. 



The sandstone does not to my knowledge contain veins of 

 ores ; these are every where in the limestone, and in those places 

 where the sandstone is the prevailing rock no mines are wrought. 

 This rock is occasionally useful as a building stone, for furnaces 

 particularly, and it sometimes occurs of a suitable quality for the 

 manufacture of glass, as at a locality four miles east of Caledonia 

 on the Farmington road. 



The lead ore occurs in various ways, frequently in horizontal 

 strata in the red clay overlying the rock ; in true rock veins, 

 which are subject to all the variations in thickness, in richness, 

 and to all the changes that the better known veins in the primary 

 rocks are; and also in vertical fissures in the limestone, either in 

 loose " chunks" in the clay which fills the^ fissures, or in regular 

 horizontal layers at intervals across them, or incrusting the walls 

 of the fissures, accompanying them as far as they are followed. 

 When the fissures open out into what appears to have been a large 

 cave, now filled with clay and mineral, the ore incrusts each side 

 of the roof and floor, while within is the clay and sometimes an 

 empty space. These caves are often of large size, large enough 

 to admit wheelbarrows or carts, and the incrustation of a foot or 

 more of galena round their walls affords no small profit to the 

 proprietors and miners. 



