54

The lower part of Figure 9 is a cross-section of a single pool. Layer
“‘a”” is composed of materials consisting of 44-3 per cent MgSQu, 1-1 per
cent Na.SQ., the remainder water. At the very bottom of this layer the
amount of sodium sulphate is, in places, 5 per cent. Layer “b’’ is of
MgSO, with 4 pec cent NasSO, and 8 per cent mud. Layer ‘‘e” is a thin
layer of black mud. Layer ‘‘d’ is formed of magnesium sulphate with 0
to 1 per cent NasSO, and 20 per cent mud. The crystals of epsomite are

66,99 ah )

- larger in layer ‘‘d”’ than in ‘‘a”’ or

Hydromagnesite about 1 foot thick is said to underlie a part of the
flat which, lying a foot or two above the lake, surrounds the lake and
extends for some distance to the north. 7

—= SY Mo Sw,

1 Fools, largely epsomite 2,3. Mud layers

a. Nearly pure magnesium sulphate. b. Impure magnesium sulphate.
c. Black muck dd. /mpure magnesium sulphate

Figure 9. Idealized cross-sections of epsomite deposit near Clinton, Lillooet. district,
British Columbia.

‘ ORIGIN OF THE DEPOSITS.

The individual deposits or pools of epsomite are basin-shaped. They
contain besides epsomite, sodium sulphate and layers of mud. In the under-
lying mud hydrous magnesium carbonates are present. These deposits
belong to the hydromagnesite, calcite, gypsum, series of deposits occurring
near them at Clinton (Figure 3) and elsewhere. The magnesium in the
deposits is derived, through the agency of sulphated waters, from the
magnesium rocks of the Cache Creek series such as outcrop in the hills near
the lake (Plate X) and is carried into the landlocked pond by underground
channels. The solutions diffuse into the lake, but upon condensation of
the lake water as the result of evaporation, the heavier brine collects at
the bottom on top of the mud and crystallization begins there at a number
of centres. Masses of crystals form around a centre and sink into the mud.

_ The process continuing, successive concentric layers with slightly larger

circumferences form on top. Successive sinking and growth cause the
formation of the basin-shaped bodies of epsomite.