168 The American Geologist. March, 1892 
never yielded gold so generally and in such profusion as the newer 
beds further west of them. I would not, however, be under- 
stood as claiming that the Mesozoic formations, even in Califor- 
nia, give as a rule richer mines than any other formation. So 
far as the evidence goes, for that region, such a generalization 
might be accepted, but we know far too little of the laws of the 
formation and distribution of the noble metals to make any rigid 
discrimination in favor of one geological horizon over any other. 
Some of the most valuable gold mines do not occur in stratiform 
rocks. The celebrated veins of Grass valley, California, which 
have been worked continuously for over forty years are in crystal- 
line granitic rocks of uncertain age. The great Comstock lode in 
Nevada, which has added so many millions to the world’s supply 
of gold as well as silver, is in crystalline rocks which, however, 
are probably altered Mesozoic beds. The gold of the Deep Creek 
region, Utah, as I have elsewhere shown, is in altered Carbonif- 
erous limestone, thus being in upper rather than lower Paleozoic. 
The best example we have of gold in the oldest rocks is found 
in the Black Hills of South Dakota in pre-Silurian strata, probably 
the equivalents of the Cambrian, Montalban, or still older sedi- 
ments. But here in these ancient strata, although the aggregate 
quantity of gold is large, the quantity per ton of rock is not. 
To use the technical phrase it is ‘‘low grade rock” as compared 
with the gold quartz rock of the California Mesozoic: 
The financial success of any gold mining operation is not to be 
taken as an indication or measure of quantity. Success or failure 
depends largely upon location, the facilities for working and upon 
intelligent common sense management. 
In conclusion it is well to note briefly the general absence of 
gold, so faras yet known, in the ordinary red beds of the Trias 
of the Rocky mountains, and Appalachians, and from all forma- 
tions where the iron is in the condition of sesqui-oxide. I donot, 
of course, refer to, or include the oxidized outcrops of formations 
where at water level the normal condition of the contained iron is 
that of prot-oxide or of its sulphur compounds. This is the 
normal state of the California Mesozoic. The auriferous forma- 
tions there are generally bluish-green and black in color, the dif- 
fused iron is in the state of protoxide, or the sulphide, and the 
formations bear no resemblance to the Trias of the Rocky mount- 
ain region or of the Appalachians. 
