49

Table Il,-analysis No. 7. It is a high grade hydromagnesite. “Analyses
made on the lower lying and yellower outcrops to the west are said to have
_ yielded results that were high in lime. The estimated amount of pure
hydromagnesite is 6,600 tons and the total for the two deposits is 13,500.

The Riske Creek deposit lies west of the Fraser about 35 miles from
the railway at Williams lake, and about 305 miles from Squamish.

CALCAREOUS TUFA.

In a railway cut at 42-Mile post, about 2 miles southwest of Clinton,
a deposit of consolidated calcareous tufa is exposed. It was not analysed,
but from qualitative tests is probably composed almost entirely of calcium
carbonate. A similar deposit on Clinton creek west of the railway bridge
contains iron, manganese, and other impurities as well as lime carbonate.
The tufa is a bedded, firmly compacted rock unlike the unconsolidated,
more or less incoherent hydromagnesite and associated deposits described
above. It is white to cream-coloured and certain of the denser beds show
many minute, glistening faces with a silky lustre. Under the microscope
it appears to be composed of particles about 0-001 to 0-003 mm. in diame-
ter with very high birefringence. Nearly all these particles show well-
developed crystal faces and the crystals appear to be equidimensional,
showing rhombs and prism faces. The material, as proved by. testing
with ferrous ammonium sulphate,! is calcite and not aragonite. The
individual beds are very thin with many irregular cavities between them,
lengthened in the plane of the bedding and showing small, somewhat
spheroidal protuberances on their inner surfaces. In certain of the freshly
opened hydromagnesite deposits very similar cavities are present, although
they are on a smaller scale, perhaps because the slightly coherent state of
the hydromagnesite mass would prevent the forming of larger open spaces.

The deposit is dome-shaped. It measures about 500 feet across in the
railway cut, where it is exposed to a depth of 17 feet. The bedding planes
are horizontal in the central part of the deposit, but outwards from there,
dip downwards toward the edges, the beds being parallel to the dome-
shaped upper boundary of the mass. Individual layers vary in thickness
from one-quarter inch to 2 feet. The upper surfaces of certain layers are
covered with wave-like corrugations resembling ripple-marks and where
these occur on inclined beds the lower edge of the corrugations is steeper
than the upper edge (Plate VIII).

The most remarkable feature of the deposit is a structure closely
simulating folding (Plates VIII and IX). In places a series of these beds
changes laterally into a bulging, pillow-like dome structure. In other
places the beds, through a varying distance vertically and for spaces of
8 inches to 2 feet horizontally, appear as if closely folded into very sharp
anticlinal forms, but between the steeply inclined axial planes of these
fold-like structures, the beds lie almost perfectly flat. The flat-lying parts
of the beds are porous, the “folded” parts are dense and traversed by
radial cracks normal to the surface. In still other places, two superimposed
sharply ‘folded’? beds are separated by an absolutely flat-lying layer of
travertine and soft clay. As seen in cross-section along the railway cut,
the “folds” are overturned towards the outer edges of the deposit. The
same layer is flat-lying and porous in one place, whereas a few inches away

1Rosenbusch, H., Mikroskopische mineraloque I i, p. 441.