APPENDIX—GEOLOGICAL SURVEY. 
430 
veins or ore deposits might not be found in sandstone as well 
as in any other rock. But when we remember that the mate¬ 
rial forming mineral veins is chemically deposited, and that 
too, only where favorable conditions for chemical action are 
presented, such as a peculiar condition of tbe wall rock of a 
fissure, or the cap rock of an opening, we see how utterly 
unfit a loose quartzose sandstone is for the formation of min¬ 
eral veins. 
But there is a point here, too often overlooked, that we 
would do well to consider, namely, that mineral veins are sel¬ 
dom found in unaltered rocks, that is, rocks in tbeir normal 
condition; but usually, if not always, in rocks that have been 
exposed to metamorphic agencies, and that have undergone 
important changes since their original formation. 
Between the physical conditions producing the changes in 
the rock, and the physical conditions producing mineral-veins, 
there are sometimes close relations. Like as the farmer pre¬ 
pares his soil before sowing his seed, so these conditions follow 
each other. And as the farmer furnishes the elements lacking 
in the soil, so nature often by metamorphic action furnishes 
the necessary qualifications lacking in the normal condition of 
rocks. Every miner and every man who has made mining his 
study knows that it is the metamorphic or altered condition of 
the rocks, not the normal, that furnishes the properties we call 
mineral bearing. Hence we find sandstone in many parts of 
the world, under varying forms of metamorphic action becom¬ 
ing metalliferous, or mineral-bearing. There are places, how¬ 
ever, where sandstone in its normal condition and lacking the 
necessary qualifications for fissures and mineral veins proper 
is nevertheless, to a certain extent, and in a very peculiar form, 
metalliferous. The sandstone of the Bleiburg (Lead mountain), 
near Commern, in the Prussian Bheinish Province, furnishes 
an interesting example of this kind. Yan Cotta, in his treat¬ 
ise on “ Ore Deposits," gives us the following account of this 
formation : 
“ The sandstones contain ores for a distance of about two miles, but are 
les3 rich towards their outer limits; the same commence near the surface, 
