ASPEN MOUNTAIN. 153 
horizon the porphyry has spread out more or less irregularly, and includes 
fragments of the shale. 
Nearly the whole of the dolomite in this downfaulted block has been 
highly mineralized, so as to form ore of greater or less richness. The 
richest ore, however, lies in irregular shoots which are parallel with the 
main faults, dipping steeply to the southwest and having a northwest trend. 
These rich shoots lie very close together, as seen in the Visino workings, 
and from them an immense amount of ore has been taken out. At the 
surface, in the middle of the block, the ore was first discovered in out- 
crop, and here $110,000 worth was taken from the great Bonnybel open 
stope, without timbering. This stope seems to occur between two parallel 
faults of the main system. ‘The richest ore is in the southwest side of the 
block, where the faulting seems to have been greatest. In the Bonnybel 
fault, which bounds the block on the east, only one pocket of ore has thus 
far been found, that in the Forest tunnel. 
The occurrence of the ore in the Bonnybel is noteworthy among that 
of the other mines of the district, in that nowhere else has the rock been 
mineralized to such a degree. In other mines there are small bodies of ore 
far richer than that in the Bonnybel, but here not only has the whole rock 
been transformed into low-grade ore, but the mineralization is in distinct 
steeply dipping shoots which cut across the formations. The explorations 
are now not far above the Parting Quartzite and there is still rich ore in 
sight, so that it is hard to tell how much farther down the ore deposits will 
extend. 
The ore itself is a mineralized, broken dolomite containing much 
barite, and so far is all oxidized. A little native silver has been found. 
Durant mine—The Durant is connected with the Bonnybel by the Visino 
incline, which in descending runs to the westward with the dip of the 
rocks. This mine is situated on the east limb of the Aspen Mountain syn- 
cline and near the summit of the Tourtelotte Park uplift, where the steep 
north face of this uplift begins to flatten in Tourtelotte Park. As the 
result of this position there occur in the mine many small fractures and 
cross faults, which complicate the structure very much and render scientific 
mining absolutely necessary. The eastern limb of the syncline becomes 
very steep a little below the surface, turning down so as to become vertical, 
and even locally overturning so as to dip to the east. After this sudden 
