55

The company controlling the deposits at Clinton has opened very
similar deposits at Kruger mountain on the International Boundary near
Oroville. These deposits were probably formed in the same manner as
those at Clinton. According to Jenkins! there are, near Oroville, two
landlocked lakes containing brines and beds of epsomite. The lakes are in
rock basins without outlet; the surrounding rocks are metamorphosed
pyritiferous dolomites and shales. Figure 10 is a cross-section of the lake
drawn according to information furnished by F. Calvert. In this figure,
layers “‘a” and “ce” are cone-shaped bodies of epsomite with a thin layer otf
mud, “b.”’ Layer ‘“d’’ is of black mud carrying 25 per cent of epsomite
with a layer of leaves ‘“‘e.’”’ Layer “‘f” is a bed of epsomite with very large
crystals. Layer “g’’ is a thin layer of gypsum underlain by a thin bed of
clay resting on “h,’”’? metamorphosed dolomites and shales. The surface
of the salt in ‘‘a”’ is lower than the top of ‘‘d.”’

aawec Epsomite with mud layer b;- d. Mud with layer of leaves e; f Epsomite
g Gypsum over clay; h. Metamorphosed dolomite, etc.

Figure 10. Cross-section of Bitter lake, Kruger mountain, Washington, U.S.A.

#3 Jenkins states that the drainage basin of the smaller lake is less than ~

one-half a square mile in area. Sulphated waters formed by the oxidation
of pyvite occurring in the surrounding rocks are presumed to have dissolved
magnesium from the dolomites. Jenkins believes that the cone-shaped
masses of salt in the upper part of the deposit were formed by crystallization
of solutions percolating upward and that the force of the growing crystals
helped to open up a space in the mud, thus forming a deposit which grew
upward with increasing width until the surface was reached. Objections
to this hypothesis are that a mass of salt forcing its way to the surface by
crystal growth would form a body with a convex or irregular rather than
flat upper surface. The flatness of the upper surfaces of the inverted
cones at Kruger mountain and the fact that the materials composing the
cones is comparatively free from the impurities that form small ridges all
around them, suggest that the bodies were formed in the following manner.

It is well known that there are cyclic changes of climate in which con-
ditions change from arid to moist and back to arid. It may be supposed
that after the formation of the rock basin by glaciers, there was a period
of aridity during which a certain amount of magnesium sulphate in solution
collected in the bottom of the basin, probably mainly through underground
channels. In this solution were also sodium and calcium. Evaporation
and consequent concentration caused the formation of the lower bed. A

succeeding cycle of greater rainfall gave rise to surface streams which |

Jenkins, Olaf P., “Spotted lakes of epsomite in Washington and British Columbia.”’ Am. Jour. Se., vol. XLVI,
Noy., 1918, pp. 638-644.

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