DESCRIPTIONS OF TIN MINES. 
47 
and magnetite. There are present, then, m this mine representatives of the three stages 
of the intrusion of granite. On this account, as well as for the reason that the workings 
have reached below the zone of superficial alteration, the Jones mine is tlnynost interesting 
and instructive place in the entire belt for the study of the tin deposits. 
The pegmatite of the Jones mine is the quartz-muscovite variety, in general coarse 
grained, but in certain places rather finely granular. The mica is usually a prominent con- 
stituent. Both dikes contain cassiterite. A shallow pit and short drift on the interfoliated 
or inclined dike exposes a narrow shoot of ore pitching not very steeply to the northeast, 
so that it passes below the drift. 
The principal workings are on the cross dike. The main shaft begins on the dike, but 
at some depth the dike bends to the south and the dike passes into the foot wall. It is 
estimated that the bottom of the shaft is at least 20 feet distant from the dike. 
Although varying in width from a few inches to 4 feet, and having a strike and dip which 
are not exactly constant, this dike is regular as compared with the majority of pegmatite 
bodies of the region. Fig. 5 gives an indication of the structure of this dike. Little nar- 
row offshoots are injected into the country rock parallel to its foliation. Slickensides are 
seen in places along the walls. An ore shoot was encountered on the surface and was pros- 
pected by means of a 40-foot shaft. The ore body was found to pitch to the west, so a 
Pegmatite Amphibolite 
Fig. 5. — Diagrammatic plan showing structure of cross dike of pegmatite, Jones mine, 50-footlevel. 
drift was run westward from the bottom of the shaft. The main shaft was then begun 
still farther west. From a point about 50 feet below the surface and perhaps 50 feet east 
of the main shaft a stope has been made slanting upward and eastward to the surface. 
The horizontal extent of this stope along the strike of the level varies from 20 to over 50 
t. It is probably somewhat greater in this dimension than the ore body on which it 
was driven. A sublevel at a depth of 60 feet and the main 100-foot level disclose the dike, 
with the ore shoot still pitching westward. At the 100-foot level the dike is about 8 feet 
south of the shaft. A drift westward from the shaft is 45 feet long and is in the ore shoot, 
whose western limit has probably not yet been reached. On this level the cassiterite is 
present in smaller grains than usual, and more care is required in following the ore body 
than where the large dark " crystals" show plainly by candlelight. At the 150-foot level 
the crosscut to the south finds the dike much broken up. It appears here almost as if 
what has been cut is not the cross dike, but the interfoliated dike, which has been opened 
on the surface to the south. There seem to be irregular, lens-like bodies of pegmatite in 
the schist, and these carry some cassiterite. Some more crosscutting failed to find the 
regular dike as followed in the workings above, and, since very soft, caving ground was 
encountered, work was suspended in the bottom. It has been learned since the writer's 
(visit that on the 60-foot level, 50 feet west of the shaft, a northeast dike, doubtless corre- 
sponding to the northeast dike known on the surface, was struck. The same dike was cut 
