2f0 The America)) Geologist. October, 1893 
Forms of Ore-Deposits. 
The ores are found in vein-like sheets in vertical and in- 
clined crevices and in cavern-like enlargements along the 
course of such crevices known as "openings." Again, the 
ores form flats or sheets extending for some distance laterally 
between the strata, but, in my experience, generally resting 
upon the comparatively impervious strata of the brown shales, 
the latter being of ten partly decomposed and forming beds of 
blue clay. 
Observation confirms in general the theoretic conclusions 
of Whitney, ( 'hamberlin, and others regarding the genesis 
and distribution of the ores. The ores everywhere present 
the same general sequence of lead-ore in the upper portions 
of the diggings, with carbonate of zinc gradually passing into 
sulphide of zinc below, which last is associated with pyrite of 
the marcasite variety. 
In the lead-region the ore-deposits are seldom referred to 
as "veins " or " lodes," although so far as they extend verti- 
cally in the formations they have what we generally term 
vein-structure to a remarkable degree. They are called 
•'crevices" or "openings," and sometimes " sheets," "pitches." 
or " runs/ 1 
Although there is locally great diversity in the ascertained 
or supposed direction of the ore-bearing crevices, varying 
from northwest and southeast to northeast and southwest, or 
from north and south to east and west, the major axis or di- 
rection of the principal groups of deposits appears to be 
northeasterly and southwesterly, approximately coincident 
with the general geologic structure of the State, as shown by 
the trend of the uplifts further north, by the direction of the 
Baraboo axis, and by the direction of the mound-formations 
— the remnants of the shales which have, for the most part. 
been swept away. 
Direction of Crevices. 
So far as my experience extends (it has been chiefly in the 
region beyond and below Shullsburg to New Diggings), the 
crevices with the northeast trend are the most common and 
persistent, and are crossed at intervals by other crevices, of 
less extent, at right angles, giving what are called " 10 
