38

An instance of a deposit formed by the action of carbonated waters on the
Cache Creek rocks, is that of a brecciated rock lying near and slightly
higher than the epsom salt lake at Clinton. This breccia occurs amongst
actinolite schists and is made up of magnesite, siderite, and opal, that is,
the products of the decomposition of actinolite by carbonated | waters.
Near Kelly lake, crystals of gypsum with yellow oxide of iron, white mag-
nesium, and iron sulphate occur in a sheared and altered zone of cearbon-
aceous argillite. "The magnesium sulphate must be in process of formation
today, for though it is so soluble that a very light rain will wash it away,
yet there is an appreciable amount of it lying in partly sheltered cracks and
cavities in the surface. In the clay banks on Bonaparte river, described
elsewhere in this report, very strongly pyritized quartzites of the Cache
Creek have been altered to gypsiferous clays. In an old mine tunnel in
these clays the writer found specimens of magnesium iron sulphates lying
loose on the floor, not in place, but undoubtedly derived from the tunnel.
Cracks in the roof were filled with a white salt resembling magnesium sul-
phate still in process of formation, for it had dropped from the crack,
which was filled with the salt, to the floor and had there formed a small
ridge of salt deposited since the time that the tunnel was excavated. At
the Chromite mine on Chrome creek, magnesium sulphate was seen forming
in veinlets in serpentine and collecting in masses at the foot of serpentine
cliffs (Plate X). These are examples of the formation of lime and magne-
sium sulphates from Cache Creek rocks by sulphated waters as outlined
above.

Deposits of calcite, also, in fractured rocks of the Cache Creek, are
quite common. The Cache Creek formation, therefore, contains all the
materials needed to form the deposits discussed here, and in addition
contains small examples of such materials near their points of origin.

oe, Manner of Deposition.

In some instances these salts have clearly been deposited at certain
- focal points by waters percolating upwards through the drift. Plate V
illustrates the mode of occurrence of gypsum at locality 7, Figure 3, at
Clinton. Analysis 7, Table IV, represents the composition of the upper
nodule; analysis 8 is of material below No. 7 taken from a section between
depths of 2 and 34 feet from the surface. By disregarding the insoluble
tter in the analyses it is seen that the white earth in the nodule and
the white streaks in the boulder clay below are composed of gypsum and
calcite in practically the same proportion of about 9 to 1. The white earth
in the nodule and in the streaks is, therefore, identical. The white earth in
the boulder clay gradually decreases in quantity downwards, and evidently
lies in very small fractures and capillary openings in the clay. Plate VI
illustrates in detail a portion of the wall pictured in Plate V and shows
the fineness of the threads of gypsum and the manner in which the amount
of gypsum increases upward. . es Zs
The extreme sharpness of the line between the upper surface of the
pure gypsum earth and the overlying black soil is remarkable. There is
no mixing of soil and gypsum, no gradation upward corresponding to the
gradation downward into the boulder clay. The gypsum and calcite have
evidently travelled upward in solution along seams and capillary openings