GEOGRAPHICAL NOTES ON THE REGION OF SILVER CLIFF, COL. 205: 
probable such a thing might seem, no evidence of the existence of distinct metal- 
lic or metalliferous zones in the interior of the earth has been gathered. On the 
‘contrary, volcanic emissions, which may be supposed to draw from a lower level 
than water could reach, are not specially rich in metallic matters, and the ther- 
mal waters which have by their deposit filled our mineral veins must have derived 
their metallic salts from a zone not many thousand feet from the surface. The 
mineral springs, which are now doing a similar work, are but part of a round of 
circulation of surface-water, which, falling from the clouds, peneirates the earth 
to a point. where the temperature is such as to drive it back in steam. This, with 
fluid water under pressure and highly heated, possessing great solvent power, 
may be forced through vast beds of rock, and these be effectually leached by the 
process. Should such rocks contain the minutest imaginary quantity of the met- 
als, these must inevitably be taken into solution, and thus flow toward or to the 
surface, to be deposited when, by diminished temperature and pressure, the sol- 
vent power of the menstruum is diminished. It is evident from these facts that we can 
not trace the history of the metals back beyond the Laurentian age. And since 
we find them diffused in greater or less quantity through the sedimentary rocks of 
all ages, and also find processes in action which are removing and re depositing 
them in the form of the ore-deposits we mine, it is not necessary to look farther 
than this for a sufficient theory of their formation. 
GEOLOGICAL NOTES ON THE REGION OF SILVER CLIFF, COL. 
BY SAMUEL J. WALLACE. 
The rough country for twenty miles east of Silver Cliff has been dry land 
through nearly all the known geologic ages. It is the southern part of an old land 
which reaches north through the state, and against which the great ocean beat to 
east, west, andsouth. This may be termed the Madre land, from the Sierra Madre 
mountain system, along which it lies, and as being the mother-land of this region. 
It was a mountain region, of stratified metamorphic granites, or granitoid 
rocks. ‘These are traversed by numerous barren leads, and some which bear val- 
uable minerals, iron, lead, gold and silver. 
The great Sangre de Cristo range, ten miles westward, is capped by a thou- 
sand feet of conglomerate of granitoid boulders, which were washed down from 
these older mountains, when that was the bed of the sea, since upheaved into the 
great range of the continent. The core and west side of that range, here, are 
eruptive granites, and also bear leads with gold, silver, copper andiron. The 
‘Tange bears other sedimentary strata, including limestones, on its flanks north 
“and south, on each side, probably of the same age as those extending south far 
‘into New Mexico, and north beyond Leadville, and attributed variously to the Si- 
| lurian, Devonian, or Subcarboniferous ages. These probably originally covered 
‘the whole range. Fossils have been brought from Hayden’s Pass, north, but I 
o not know of what age they were. 
