54 Geological and Mineralogical Character of [Feb., 



The metallic veins, though not of very frequent occurrence, in 

 crossing the mineral belt, yet seemed to be arranged iu groups. At 

 Dufktown, Tennessee, there are at least seven or eight distinct veins 

 of copper, running generally parrallel to each other, and limited in 

 their North range to a width of about three miles. These metalic 

 veins are usually composed of three distinct portions. The upper 

 part is a mass of light porous hydrated per oxyd of iron, to which the 

 miner's term gossan, is universally applied. This gossan is found on 

 the surftice at many points along the outcrops of the veins, espe- 

 cially on the knolls and ridges. Sometimes it occurs in great banks 

 or blocks, scattered over a space of fifty or a hundred feet wide, 

 while at others but little of it is to be seen. The depth to which it 

 extends in the vein is variable, being often from seventy to ninety 

 feet on the high grounds, but in the valleys perhaps about twenty- 

 five. The depth appears to be the same as that to which it is nec- 

 essary to go — in digging wells, for example — to reach water. 



Immediately below the gossan there occurs a bed or mass of dark 

 or black copj^er ore, some of which contains as high as fifty per cent, 

 of metalic copper, but averaging from sixteen to twenty. Its verti- 

 cal thickness is variable ; at some points it swells out in great masses 

 many cubic yards in volume ; then again it becomes a thin, irregular 

 layer. The average thickness, perhaps, is between two and three 

 feet. In width, of course, it varies with the veins, which at some 

 points are fifty and sixty feet wide, though the average is much low- 

 er. This bed of black copper ore has furnished, as yet, nearly all 

 the ore shipped from the mines in Tennessee.* 



The lowest, or third portion of these veins, is composed of a 

 compound sulphuret of iron and copper. The two minerals are com- 

 mingled in distinct chrystals, the sulphuret of iron, however, greatly 

 predominating in the upper portion, while the sulphuret of copper, 

 or the yell'iJO copper, as it is called, increases in descending upon 

 the lode.f This portion of the vein is continuous downward, and 

 has no termination, probably, except in the great interior source of 

 metalic veins. 



Thus, then, these metalic veins are composed of three parts : the 

 Iron gossan, the hlack copper ore, and the compound sulphuret of Iron 

 and Copj>er. The last named ores are called, by the miners, the ' ar- 

 senical iron,' when the sulphuret of iron predominates. 



* Pvof. Safford. 



t Tlie tciTii lode is applied to any regular vein, whether of metals or minerals or both 

 combined. 



