THE MINING AND QUARRY INDUSTRY I9QI2 103 
tale seams occurring nearly always on the southern or footwall 
‘side of the latter. The association of the silicates and sulphides 
is of considerable interest for the study of the derivation of the 
ores. 
The zinc appears to have been introduced into its present place 
by underground circulations and deposited mostly as a replacement 
of the limestones, very little as a filling of open fissures. The view 
as to the secondary nature of the deposits is supported by their 
variable form, which ranges from narrow seams or bands to lenses 
and again to very irregular shapes. The seams, in places, also break 
across the bedding of the limestones. The horizon of the ore 
varies considerably within the limits of a single locality as at 
Edwards and in such a way as to be hardly explainable by struc- 
tural disturbances of once continuous seams or beds. 
That the ores have replaced the limestones is indicated by the 
lenticular or quite irregular forms assumed by the bodies, as above 
noted, by the gradation along the borders from the rich sulphides 
to leaner material and finally to barren limestone, and further by 
the absence of banding in the arrangement and of drusy cavities 
which characterize the fillings of open spaces. The ore body opened 
by the southern shaft at Edwards, however, has quite well-defined 
parallel walls as seen near the surface which may mark a fissured 
zone or channel followed by the ore-bearing solutions. 
The specimens frequently exhibit nodules of talc and serpentine. 
These range from very small size—a fraction of an inch in dia- 
- meter —up to nodules measuring a foot or more across. They 
are practically barren of sulphides, except such as have been frac- 
tured when the ore may be seen to extend into or across the nodules, 
following the seams. The nodules more often than not consist of 
a tale core with a surrounding shell of serpentine. The talc has a 
massive appearance in the hand specimens, not fibrous like the usual 
product of the tale mines in the vicinity; whether it has originated 
from alteration of tremolite or has possibly been formed directly 
from solutions in the period of metamorphism of the limestone can 
not be stated at this time. At any rate, the mineral associations in- 
dicate that the nodules, so far as represented by the talc cores, ex- 
isted before the ores were deposited, though the serpentine is in 
part of later formation. 
The serpentine which encrusts the nodules belongs to the massive 
variety and shows no evidence of being pseudomorphic after an 
anhydrous silicate. Its relations rather suggest a reaction product 
