176 GEOLOGY AND GOLD DEPOSITS OF THE CRIPPLE CREEK DISTRICT. 
from the El Paso mine, level 3, C. Iv. & N. vein, show that an original crust of 
celestite is converted into pseudomorphs of quartz coated by quartz crystals on 
which a still later generation of fluorite and lastly quartz is again deposited. 
At the Blue Bird mine a fissure filling of “purple quartz,” a fine-grained aggre¬ 
gate of quartz grains in which still smaller cubes of fluorite lie embedded, has been 
broken, and the new cementing material consists of various forms of quartz, chal¬ 
cedony, and opal, usually appearing as a yellowish or white flinty material. One 
specimen of this shows under the microscope a network of bars of cryptocrystalline 
silica, the interstices between which are filled by clear radial chalcedony, including 
a few grains of fluorite. Some of this silica bears evidence of being pseudomorphs 
after a doubtful mineral now dissolved. Replacement of dolomite is shown by 
specimens from the Orpha May dump. Quartz crusts are here covered by small 
pyrite crystals and sharply defined primary rhomboliedrons of dolomite, all of 
which are coated by a yellow fiber of opal, in most cases forming a thin, empty 
shell, the original mineral having been dissolved. Like the tellurides, however, 
celestite, on the whole, is particularly characteristic of the medial vuggy portions 
of the veins. Chalcedony and opal belong to a late stage of the vein formation 
and occur characteristically as films or botryoidal incrustations in the vugs. 
In the narrow veins and seams which cut through the altered rock near the 
fissures a very definite order of succession is often noted. Adularia in well-devel- 
oped crystals or crystalline aggregates is the first mineral deposited and coats the 
walls, while the interior of the vein is filled with granular quartz, in which as the 
latest product rhombohedrons of dolomite are contained (PI. XVII, B ). In latite- 
phonolite of the Findley mine the succession is adularia (oldest), dolomite with 
calaverite, fluorite, quartz (youngest); the surface of the quartz is dull and cor¬ 
roded. Wavellite is a primary vein mineral and in places forms tiny filled veinlets 
accompanied by pyrite. The walls of these veinlets are lined with adularia. 
To speak very broadly, the vein filling began by the deposition of adularia 
and the base sulphides, such as pyrite, sphalerite, and galena ; then followed deposits 
of quartz, fluorite, and dolomite, sometimes repeated, and toward the last tellurides 
and celestite, followed in some places by repeated deposition of quartz and fluorite. 
The closing chapter is in some veins represented by extensive deposition of quartz 
and chalcedony, frequently replacing the celestite and coating all other constitu¬ 
ents. Molybdenite is usually intergrown with pyrite and zinc blende, indicating 
that it is one of the older vein minerals. 
STRUCTURE. 
To a certain extent the larger structures of the lodes have been described in 
the section devoted to the fissures. The present section relates particularly to 
the modes in which the various minerals are arranged within individual fissures. 
The Cripple Creek veins are characterized in general by a vuggy structure. 
Some fissures are solidly filled with vein matter, but this, on the whole, is not common. 
Usually the walls of the fissures are covered with crystalline crusts which have 
grown together here and there along the medial plane of the vein, having numerous 
cavities lined with projecting crystals of quartz, fluorite, and other minerals. In 
most cases the crusts are comparatively thin and the vugs narrow. In some lodes 
