APPENDIX—GEOLOGICAL SURVEY. 
443 
it is barren where it is exposed to view on the north of the 
lead district.I would like to put a nail in this error right 
here by saying, that while it is evident that certain kinds of 
rock present more favorable conditions for mineral veins than 
others, it is also evident that they are not the cause, but the 
conditions that favor the cause by which mineral veins are 
formed. It is safe perhaps to say that mineral veins are al¬ 
ways found in connection with physical forces acting from be¬ 
low ; forces, in their origin independent of the rock in which 
the veins are found. And if one class or kind of rock traversed 
by these veins is richer in minerals or ores than another, it is 
because in this class or kind of rock, these forces found more 
favorable conditions for ore deposits. It is only in the pres¬ 
ence of these forces that any kind of rock is metalliferous, and 
apart from them every kind is alike barren. Suppose we ap¬ 
ply the rules to the upper magnesian by which certain parties 
have condemned the lower magnesian, may we not with equal 
propriety condemn it with the same class of evidence? 
If, previous to the discovery of our lead mines some one had 
been sent out to make a geological survey of what is now 
known as the lead district, and had commenced his work in 
Eock and Jefferson counties to the east of those heavy belts of 
mineral ranges extending through Grant, La Fayette and Iowa, 
into Green and Dane, where the same kind of rock—the 
upper magnesian—is the surface rock; or if he had 
extended his exploration, even into Green and Dane, con¬ 
fining his examination to the eastern side of these counties, 
he would not have found anything that-would justify him in 
pronouncing it a metalliferous, or mineral bearing rock. And 
if from this standpoint, within two or three miles of what has 
since proved to be a very rich lead district, he had pronounced 
the upper magnesian limestone a barren rock from evidences 
afforded on the eastern side of the lead district, he would be 
entitled to as much credit for sound judgment as those who 
condemn the lower magnesian as a barren rock from evidences 
afforded on the north side of the lead district; for both are 
