substance occurred around the fragment, while calcite was outside of all (fig. 35).
These
enclosures occur of all sizes, from fine powder to very large masses.
The largest masses are seen only at the top of the mine, and are made
of shale ; they are called ' floating reef.' In regard also to smaller
fragments, shale is most abundant at the top of the mine, and less
abundant the deeper we penetrate. Bounded fragments of granite,
mica-schist, and quartzite are found, though rarely, and fragments of
diabase also occur. All seem to have been carried upwards.
Chemical Composition of the Ground-mass.—Almost
all of the rock is soluble in acid, a small residue of garnets,
biotite, bronzite, perovskite, ilmenite, chromite, &c, remaining.
By repeated treatment with hydrofluoric and
