258 The Amerlcayi Geologist. April. i897 
The mineral association is usuallj' iron, lead, silver and 
zinc with a predominance ol' sulphides. The quartzite is not 
rarely altered near the contact with the line to a chloritie si- 
licioiis schist with epidote and calcite. This phase is called 
"greenstone" hy miners. At various places dioritic intrusions 
penetrate the qiiartzites and cause local and perplexing dis- 
turbances in the rather uniform stratigraphy. We may pre- 
sume that the lead in this region has been derived from more 
or less generally disseminated deposits throughout the lime- 
stone, and the probability is that it was originally in the form 
of galena. The present situation and composition of the 
lead is, however, to be ascribed chiefly to the influence of per- 
colating waters with the cooperation of metamorphism. At 
this lowest lime contact both factors assisted. The limestone 
is between seventy-five and one hundred feet thick, and has 
been greatly altered in so far that it forms a coarse white 
marble in several localities. The effect of metamorphism is 
seen not only in the crA^stallization and decolorization of the 
lime, but also in the segregation of the silicious matters as 
bands of chert or flint. The lower portions especially are si- 
licious and metamorphic. The fossils have usually suffered 
from metamorphism, though occasional crinoid stems occur. 
The location and association point to a middle Carboniferous 
age. The ore is usually near the contact, though it may be 
several feet distant. In at least two horizons within this 
limestone other ore concentration has occurred, but only in 
certain localities do they become important; yet where this is 
the case they are often very valuable, since the ore is collected 
in old watercourses lying in plains of seepage, under condi- 
tions for solution of lime and redeposition of ore. The lower 
contact, as stated, contains chiefly sulphides, yet the lead is 
frequently reduced to sulphate or altered to a carbonate in 
such situations as have permitted a free percolation of waters 
from higher deposits. It is interesting to note that the mines 
opened along the summit of the range where cutoff from such 
supplies are usually of small value, being poor in ore, which is 
here chiefly a sulphide. The silver value is, it is true, higher 
than farther down, but as this is subordinate practically to 
the lead, it does not repay for a lower lead contact and the ab- 
sence of large cavities with carbonate of lead. This difference 
