164 
AMERICAN GEOLOGY. 
of gold, neither can they be employed to prove that a change 
of climate took place about the time the Mammoths of this 
country became extinct. 
I have already had occasion to state the facts relative to 
comparative richness of the gold veins at considerable depths. 
This question is economically one of great importance. Capi¬ 
talists in this country are now pursuing their schemes and 
plans for working gold mines at all accessible depths. They 
make no distinction between auriferous and cupreous veins, 
neither do the auriferous veins appear at all analogous to the 
staniferous veins of Cornwall, which were said to be stanifer- 
ous upon their backs, but cupreous in the main parts of the 
lode. Here the gold accompanies the yellows, as the sulphuret 
of copper was called in Cornwall, without giving place to it 
as the tin lodes referred to. 
AGE OF THE GOLD TEARING ROCKS OF THIS COUNTRY. 
§ 100. The talcose slates, mica slate, hornblendic gneiss, etc., 
which are traversed by auriferous veins, belong to a period 
which preceded the deposition of all the hydroplastic rocks of 
this country. The evidence which sustains this position is of 
two kinds. 1. Evidence of composition and derivation. 2. Of 
superposition and succession. 
1. The oldest sediments belong to the Taconic system. The 
talc and mica of the gneissoid granite enters into the composi¬ 
tion of the limestone. A peculiar bluish tinted quartz of the 
same rock enters into the composition of the quartz rock at the 
base of the Taconic system. These minerals are distinguishable 
from other varieties of the same species. So it is not less cer¬ 
tain that the materials of the Taconic system are carried up 
into the Silurian. Thus a stratified limestone is found in the 
Potsdam sandstone at Chazy. The Taconic slate enters into 
the composition of the lower part of the calciferous sandstone. 
2. The quartz rock of the Taconic system rests unconforma- 
bly upon the gneiss of the Green Mountain range, or its gneiss- 
