wnsome.] STRUCTURE OF THE LODE ORES. 91 
sopyrite in the middle with tetrahedrite on each side, the latter fading: 
3ff into the altered country rock. 
S. Brecciated structure. — Ore formed at an earlier period of deposi- 
tion has been broken into angular fragments by renewed movement 
ilong the fissure, and reeemented by fresh deposition of the ore or 
gangue. 
Ore so shattered as to come under this head has not been noted as 
a conspicuous feature of any important deposit, although some brec- 
siation can often be detected. The structure, however, is best exem- 
plified by material from the dump of the Red Cloud mine, in which 
in original deposit of radially fibrous pyrite has been broken up and 
held together by a younger accumulation of vein quartz carrying a 
little sphalerite and galena (PL XI, 0), and also by vein filling from 
ilic Polar Star and Palmetto mines. In the Red Cloud occurrence 
not only have the concentric shells of pyrite been broken up, but in 
some cases exceedingly thin coatings or sheets of the sulphide have 
been floated or moved ou1 into the quartz, and in the polished speci- 
men from which PI. XI, C was made these delicate curved films 
embedded in the quartz resemble the finest cloisonne work of the 
Japanese. 
//. Cellular structure. — The quartz or other vein material has crys- 
tallized as a mass of irregularly intersecting septa, leaving numerous 
irusy cavities separated by relatively thin walls. 
This is not a structure characterizing any important ore deposit, 
and was not seen in place. Bu1 it is of interest in view of the pos- 
sible light that it may throw on the processes by which the vein- 
forming materials are deposited. The structure is best exemplified 
iby fragments on the dump of the Pride of Syracuse mine and on an 
upper dump of the Empire* group, Sultan Mountain. In the latter 
case the septa are composed chiefly of sphalerite and galena, and the 
cells are Lined with drusy quartz and in some cases filled with rhodo- 
chrosite. Beautiful little crystals of amber-colored sphalerite and of 
let railed rite were observed in some of the cells, implanted upon quartz. 
It is possible that this cellular structure may have resulted from some 
kind of pseudomorphous replacement coupled with the solution and 
removal of some unknown mineral. 
5. Spherulitic structure. — The quartz of a vein has crystallized in 
prisms, often imperfectly formed, which show a marked tendency to 
group themselves in radial fashion about local centers of crystalliza- 
tion. It is not intended to treat specially under this head such min- 
erals as tremolite, which exhibits characteristically a radial structure. 
A rough spherulitic crystallization, previously described by Pur- 
ington, 1 was noted in the gold quartz of the Tomboy mine and, in 
connection with banding, in the Camp Bird lode. It is also a notable 
feature of the North StaV lode, where worked in the Dives mine (see 
Preliminary report on the mining industries of the Telluride quadrangle, Colorado: Eigh- 
teenth Ann. Rept. U. S Geol. Survey, Pt. Ill, 1898, p. 840. 
