May, 1904. GEOLOGY OF WESTERN MEXICO—FARRINGTON. 21% 
rious times to extract these metals from the mountain. Birkinbine 
mentions one shaft 70 feet deep made through solid ore on the north 
side of the mountain, with drifts extending from its bottom,* which 
was probably sunk with the hope of finding precious metals. In 
the iron ore of the Murca-ranch, a deposit of similar origin to the 
Cerro Mercado and connected with it, Witherbee reports} that as 
much as g ounces of silver and o.5 ounces of gold have been found. 
The first serious attempt to use the deposit as a source of iron 
seems to have been made in 1828, when an English company under 
patronage of the Governor of Durango, established some works 
on the bank of the Rio Tunal, five miles south of Durango, on a site 
known as Piedras Azules. Motive power was secured by a dam 
across the river, and a blast furnace was erected. First attempts 
to obtain iron from the ore were however unsatisfactory, and the 
project was soon abandoned. In 1834 a new company took the 
matter up and by constructing a blast furnace of different type, suc- 
ceeded in obtaining a product of 5,000 to 8,000 pounds of iron a week. 
With some intermissions a small output of iron from these works 
has been maintained ever since. About 1882 a larger plant, shown 
in Plate LXIX., was erected close to the western end of the mountain. 
Successful operations were not conducted here until 1888, and only 
within the last five years has a steady production been maintained. 
A full description of the plant and of the iron produced is given by 
‘Witherbee.t{ The fuel used is charcoal, or charcoal and coke, the 
charcoal being made largely from the mesquite. For flux, limestone, 
obtained about twenty-five miles distant on the line of the Mexican 
International Railroad is used. The iron produced is said to have 
exceptionally good chilling qualities and to be very strong. | 
Besides the use of the ore as a source of iron, it has been found 
valuable as a flux for the smelting of lead, and is employed extensively 
for this purpose in various smelters in Mexico. Such a use of the 
ore began with the advent of the railroad to Durango in 1893, and 
since that time more than 400,000 tons have been so employed. 
Several well-defined mineral species occur upon the Cerro Mercado 
and have been more or less described. 
Chrustschoff§ reports the following: magnetite, hematite, 
quartz as rock crystal and amethyst, chalcedony, opal, phenacite, 
pycnite, fluorite, and garnet. The magnetite is described as occur- 
*Trans. Am. Inst. Min. Eng., Vol. XIII., p. ror. 
*Trans. Amer. Inst. Min. Eng., Vol. XXXII., p. 158. 
tTrans. Amer. Inst. Min. Eng., Vol. XX XII., p. 158. 
SOp. cit., pp. 44-50. 
