244 ' APPENDIX. 



feature in the landscape of Wisconsin, are evidence of the 

 denuding action to which, under the cnimbhng hand of time, 

 the surface of our globe is continually subjected, and which 

 the more durable siliceous masses of these hills of flint have 

 been enabled partially to resist. 



" The northern boundary of the Wisconsin lead region is 

 nearly coincident with the southern boundary-line of the blue 

 limestone where it fairly emerges to the surface. No disco- 

 veries of any importance have been made after reaching that 

 formation ; and when a mine is sunk through the cliff lime- 

 stone to the blue limestone beneath, the lodes of lead shrink 

 to insignificance, and no longer return to the miner a profitable 

 reward for his labor. Indeed, the small quantities of lead 

 ore which have occasionally been found in the blue limestone, 

 occur in veins not much thicker than writing-paper, which 

 have insinuated themselves into the slender streams of the 

 stratification. This coincidence between the northern bound- 

 ary of the productive lead region, and that of the cliff limestone, 

 is an example of the practical utility and application of the 

 geological divisions of the different formations. Even if not 

 a single shaft had ever been sunk in Wisconsin, it might have 

 been predicted, with probability, that this change in the 

 formation would be strictly accompanied with a corresponding 

 change in the productiveness of the lead veins. 



" Mr. Carne has observed, regarding the metalliferous veins 

 of Cornwall, that it is a rare circumstance when a vein, whicli 

 has been productive in one species of rock, continues rich 

 loner after it has entered into another ; and this change, lie 

 adds, is even remarked when the same rock becomes harder 

 or softer, more slaty or more compact. Hence it was very 

 unlikely that the Wisconsin lead ore, so rich in the cliff lime- 

 stone, should retain the same rich character in the blue lime- 

 stone, even liad the structure of this last been equally adapted 



