412 
MINERALOGICAL GEOLOGY 
any of the descriptions. It is a phenomenon which is particularly 
well displayed in several of the borate fields, and especially 
in the White Basin of southern Nevada. In one instance the 
inclined strata are shifted horizontally so as to separate the two 
parts of the borate bed over 300 feet. 
The slips are disposed obliquely to the dip and strike, about 
midway between the two, or about 45 degrees. Although the 
direction of the movement is horizontal the dislocations are 
manifestly due to relief of tortional stresses, perhaps set up when 
the great block now occupied by the White Basin was faulted and 
depressed 1000 feet or more. These tortional faults sharply cut 
off both the beds of borate crystal and the associated laminated 
clays and sandstones. These features are, of course, not dis¬ 
played at the surface of the ground because obscured by weather¬ 
ing of the deposits and on account of the over wash. But they 
are clearly shown in the mine tunnels, a hundred yards or so be¬ 
neath the surface. In the mines the fault phenomena are so 
clear and fresh that they are fit objects for photography. 
Were the borate beds really mineral veins in the true sense of 
the word they would have been developed as such after the tilting 
of the strata in which they occur, and at or after, the date of the 
faulting. There are not the slightest evidences of any of these 
happenings. The borate beds were without question colemanite 
crystal at the time of their faulting. Nodules and individual 
crystals are sharply chopped off by the slipping. 
Moreover, there appears to be a secondary deposition of cole¬ 
manite which doubtless originated from the solution by the rains 
of the inclined) ore-body at the surface of the ground, and which 
followed down stratification planes. Where the faults were 
slightly open it was redeposited in a continuous sheet, an inch 
or two thick, passing directly across the bedding planes of both 
the original colemanite and the associated shales and sandstones. 
These vertical slabs of secondary colemanite are easily distin¬ 
guished at a glance from the original beds. They are composed 
of fine, long, closely appressed, needle crystals disposed at right 
angles to the fault-planes, and ensemble resemble the thin veinings 
of satin-spar which traverse the red shales occurring 100 feet 
beneath the borate beds. 
In a single cubic yard of the borate-bearing deposits there are 
