SOUTH AFRICA AND ITS DIAMONDS. 
173 
drainage-system were arrived at ; portions of the old high-level 
alluvium being left undisturbed on those stable portions of the 
valley-floor that resisted the wear and tear of denudation. If 
this be so — and it is likely enough — the precious gems brought 
to their places by the old system of drainage of the former 
high-level flats still lie amongst the remnants of local debris 
and ancient drift on the Kopjes, which remain like the navvy’s 
66 dead-men ” of excavated plains, and in the fallen talus and 
running sand and gravel of their slopes, whilst few turn up at 
lower levels. 
Nevertheless, there must be places further down the valley,* 
probably as “ pockets,” or patches of small extent, in or near 
the present river channel, into which the hard and heavy gems 
have been sorted (like gold-dust or tin-stone) from amongst the 
miscellaneous sand and gravel. Whether or no it will be worth 
while to cut off some bends in the river by short cuts, and work 
over the drained river-bed, energy and experience will probably 
some day prove. 
But whence came the diamonds at first ? And, if their origin 
can be traced, will it be profitable to look for them in their 
native matrix ? 
All the world knows that diamonds, whether in India,. 
Borneo, Sumatra, South Australia, the Ural, Algiers, California, 
the United States, or Brazil, are got from alluvial gravel 
derived from more or less distant mountains. In Brazil only 
have these gems been found in their native beds, namely, in a 
granular quartzose schist (itacolumite), and some other schists 
(micaceous, chloritic, talcose, hornblendic, and argillaceous) 
associated therewith. These, together with some accompanying 
limestone bands, evidently represent, in metamorphosed (highly 
altered) conditions, some very old sandstones, clays, shell-beds,, 
&c., such as constitute any one formation of marine and fluvio- 
marine deposits. The diamond crystals that occur in these 
Brazilian schists may also be, and indeed are always regarded 
as being, the results of some of the changes that have affected 
the strata in question ; and they may represent the carbon of 
old carbonaceous deposits, separated and purified from hydrogen,, 
clay, and other matters, whether within the original mass of 
the strata, or sublimed through pores and fissures from still 
more deeply seated sources of carbon. 
It was suggested by the late Dr. Bubidge that the direct 
heat and pressure of volcanic dykes passing through coal-beds 
might bring about a change of hydrocarbons, producing pure 
carbon ( = diamond), as they have changed certain coal-seams 
See the foregoing footnote. 
