MINES OF RAVEN AND GUYOT HILLS. 
335 
dike is seen in the Anaconda-Raven tunnel, just east of the Tornado shaft. It is 
here at least 100 feet in width. It is probably cut also in the north end of the 
Elkton level 5, north of the Tornado shaft, but this point could not be reached 
from the Elkton shaft at the time of visit. On level 7 this dike is probably cut in 
the main Walter drift north of the Tornado shaft and in the Raven drift, but as 
no particular search for it was made at these points at the time of visit, it was not 
noted. A west crosscut, however, 150 feet north of the Tornado shaft, enters a 
mass of phonolite about 100 feet west of the main drift, which is probably this 
same dike. It will be noted that this dike practically marks the northern limit of 
the Walter pay shoot. As the Walter lode enters the dike from the south the 
fissures become more regular and contain no ore. 
A smaller dike of phonolite with a general northwesterly strike is cut by the 
Walter lode about halfway between the Elkton and Tornado shafts, and conse¬ 
quently near the point where the Walter lode and Raven dike diverge. This dike 
was observed on levels 5 and 6 and seems to dip to the northeast. 
Another important body of phonolite is exposed on level 7, about halfway 
between the Elkton and Thompson shafts. The exact outlines of this body can not 
be determined from existing workings, but it apparently has the general form of a 
small sill or laccolith about 200 feet in average diameter and probably not more 
than 20 to 30 feet in thickness. This mass is considerably fissured and shattered, 
and its contact with the inclosing breccia is seldom well defined. Between this 
body of phonolite and the Elkton shaft occur a number of small masses of phonolite, 
but it could not be determined whether they represent somewhat shattered intru¬ 
sions or are merely isolated fragments in the breccia. A number of phonolite dikes 
are cut in the Anaconda-Raven tunnel in its course through Raven Hill. They 
are of the usual type, and no special study was made of them. 
Granite, breccia, and phonolite are all cut by the Raven or Elkton basic dike, 
which ranges from a fraction of an inch up to 6 feet in width. The average width 
is probably about 3 feet. The Raven dike is exposed at a number of points near 
the surface of Raven Hill, in the upper and lower Raven tunnels, in the Anaconda- 
Raven tunnel, and in the main Elkton workings. One of the most interesting fea¬ 
tures of the dike is its sharp change in course from S. 20° W. to south, where it 
joins the Walter lode. The dike is irregular at the turn, splitting and inclosing 
horses of breccia. Another notable characteristic is the manner in which the dike, 
after being followed for perhaps several hundred feet, gradually becomes narrower 
and finally disappears, though one or more fissures usually continue on beyond the 
point of disappearance of the basalt. Crosscuts into the walls at the point of dis¬ 
appearance usually result in the recovery of the dike, or, rather, of another dike 
belonging to the Raven dike zone. This behavior is well shown in the Anaconda- 
Raven tunnel, particularly where the dike, as it is followed southward, cuts the 
Tornado phonolite dike. After penetrating the phonolite for a few feet the dike 
pinches out. About 40 feet to the west another dike is cut, which also pinches out 
in the phonolite about 100 feet south of the point where the first dike disappeared. 
About 30 feet west of this dike is a third, which continues southward as the main 
Raven dike. A similar behavior may be noted on level 7 of the Elkton, between 
the Elkton and Thompson shafts. The Raven dike, at a point about 75 feet south 
