LENADO. 201 
surface, making about 200 feet. In places the ore was 40 feet thick, and 
laterally it ran along under the fault for as much as 300 feet. This ore 
contained much lead, a moderate amount of silver, and not much zine. 
The ore in the Aspen Contact mine, therefore, occurs in two chief 
zones, which are also fault zones; one at the contact of dolomite and 
shale, and one at the contact of dolomite and quartzite. Along both of 
these zones the ore is excessively broken up, and some of the very richest 
is in the finely ground fault material. Thus the ore does not seem to have 
formed in place, but to have existed previous to the fault; and as the 
faulting has been very extensive, the ore may have been carried a consid- 
erable distance. Pl. XLIII, B, is a cross section of the Aspen Contact 
mine, showing the occurrence of the ore and the various geological 
features which have been described. 
The average ore is very high in zinc, generally containing much lead 
and a comparatively large amount of silver. Barite, on the other hand, 
which is such a common gangue mineral in other ores of the district, is 
very rare. 
LEADVILLE MINE. 
The geological features exposed in the Leadville mine are substan- 
tially the same as those in the Aspen Contact. The two branches of the 
main Lenado fault are cut in this mine, the first being between the shale 
and the dolomite, and the second between the dolomite and the quartzite. In 
the northwestern part of the mine, however, the steeply dipping Cambrian 
quartzite on the south side of the fault is overlain conformably by the 
Silurian beds, so that west of this point there is Silurian dolomite on both 
sides of this fault, and it becomes hard to trace. 
In the Leadville mine there have been two chief ore bodies developed, 
both being, as in the Aspen Contact mine, in fault zones. One body was 
continuous with the main body of the Aspen Contact, lying between 
quartzite and dolomite in the more southern fault; and, as in the Aspen 
Contact, the ore was a lead and zine sulphide, with some carbonate. The 
other main ore body lay in dolomite not far from its contact with the shale, 
and had a maximum width of 8 feet, from which it pinched in places down 
to a mere seam. In appearance this ore is like a soft mud, being blue- 
black, or more generally brownish blue, in color. As the so-called “tale” 
of the miners is often a triturated limestone, so this soft mud ore seems to 
