they
are mixed, are called "floating reef" to distinguish them from the
walls of the funnels which are termed simply " reef." The inclusions
which differ from the reef are called " exotic fragments."
The
bowlders of floating reef, though occasionally rounded, usually have
sharp corners and edges, showing no signs of attrition. They were more
abundant in the upper levels of the pipes, but are found in irregular
quantities at all depths. In places, the carbonaceous shales were met
in such quantities that fire-damp, similar to the dangerous gases of
the coal mines, was encountered.
The
diamondiferous material filling the pipes has been variously termed "
serpentine breccia," " volcanic tuff or agglomerate " and later, the
name " kimberlite " was given to it by Prof. Henry Carvill Lewis, and
as that is most generally used, reference to it will be made under that
name. The kimberlite itself though comparatively soft, is harder in
some places than in others. It takes twice as long to weather the De
Beers kimberlite as it does that from the Kimberley, and much of the
Premier kimberlite needs no weathering, but goes direct from the mine
to the washers. It is somewhat soapy to the touch and it can be
scratched with the finger-nail, but it has a quality which makes it
difficult to work with the pick. It separates easily under an edge
tool, however. The various analyses made, agree in the main, the
differences being unimportant. One from the Kimberley mine by Prof.
Maskelyne and Dr. Flight gave:
