kansomk] METHODS OF MINING AND TREATMENT OF 0RE8. 39 
and different statesof preservation are found in juxtaposition, break- 
ing the continuity which is normal where the formations were noi 
thus dislocated. 
Landside action of similar character has been very prominent aboul 
Rico, in the heart of the Rico Mountains. 1 The result is to produce 
broad topographic forms of rather gentle outline, modified by many 
small ridges, knolls, and trenches. Such fractured material is now 
necessarily in process of further disintegration. Indeed, certain parts 
of the landslide area adjacent to Ironton Park have been so smoothed 
out by the ordinary creeping down the slopes of the much-fractured 
rock that the landslide character is rather obscure. Landslide ad ion 
on so gigantic a scale is at present attributed to violent earthquake 
shock. Only some such violent local force seems adequate to explain 
the enormous slides of the Telluride quadrangle, and the explanation 
is most plausible in view of the volcanic history of the region. 
METHODS OF MINING AND TREATMENT OF ORES. 
It is not proposed in this section to go into an exhaustive account 
of mining methods and metallurgical processes. Such a discussion 
would be outside the scope of the present report and would necessitate 
the collection of detailed data of a kind not contemplated in planning 
geological field work. A brief statement of methods a ml approximate 
costs may, however, be of use to readers having no practical knowl- 
edge of this district or of the modes of procedure followed in it. 
Owing to the exceedingly rugged character of the country, the 
larger mines, with the exception of those in the Red Mountain dist rid , 
are almost all worked through adit tunnels. Although involving, as 
a rule, greater initial expenditure, and, in the case of crosscuts, 
necessitating much "dead work," such adits have for large mines 
undoubted advantages in this region over shafts. They obviate the 
need of pumping, and when, as is commonly the case, t here is vert i ,-al 
connection with the surface through old workings, t hey great Ly simpli I'v 
the problem of ventilation. In a region so elevated as the San Juan 
an adit tunnel possesses great advantage in that it allows the mine 
entrance and buildings to be placed as low down as possible, where 
they can be better sheltered from the winter snow, and where water 
and timber can be more readily utilized. In several of the larger 
mines, such as the Silver Lake and Tomboy, shafts are sunk from the 
adit levels, and hoisting and pumping machinery are installed in 
underground stations. 
The levels are usually, although not uniformly, about 100 feet 
apart, and the ore is worked out by overhand stoping. It is usually 
allowed to fall on canvas and roughly sorted from the waste. Tim 
stopes are sometimes left open, sufficient timbering being carried up 
Geology of the Rico Mountains, Colorado, by Whitman Cro^s and Arthur Coe Spencer: 
Twenty-first Ann. Rept. U. S. Geol. Survey, Pt. II, pp. 129-151. 
