But
as the cutting passed farther and farther down through the reef-circled
funnels without disclosing any barren stratum or break in the body of
breccia, the surmise rose gradually to the point of conviction that the
funnels were craters of extinct volcanoes, filled by successive
eruptions of steam or gas under great pressure with a diamantiferous
breccia, carrying fragments of volcanic and sedimentary rocks and
crystals of many kinds of minerals. This conclusion, however, was
hardly more than one of several varying assumptions in advance of the
thorough researches and analyses of later years, when the prosecution
of deep mining works determined positively the existence of craters,
the character of the breccia, and the composition of its encasing reef.
So the progress of mining on the Diamond Fields was long a hesitating
and tentative advance, groping step by step into the depths of the blue
ground.
After
the device of staging and hoisting ropes had solved, for a time, the
problem of open excavation in the Kimberley mine crater, and the caving
of the blue ground was no longer a terror to the diggers, the
collection of water in the pits was a serious annoyance. Most of this
water was surface drainage,
