130 THE DIAMOND MINES OF SOUTH AFRICA
age,
whose lectures I had the privilege of attending. But it was not until I
had examined a diamond mine in South Africa and speculated upon the
apparently irreconcilable phenomena attendant upon the origin of the
diamond in its matrix, that the practical application of Faraday's
discovery began to dawn upon me. ' Hold out your hand,' said he, at the
close of the lecture that fairly electrified the world of science, as
with a loud hiss a snowy substance, burning like a coal but in reality
intensely cold, escaped into the palm of my hand from the strong iron
vessel in which, with a pressure of fifty atmospheres, he had liquefied
carbonic acid gas — the very gas resulting from the combustion
of the diamond, consisting of one atom of carbon and two of oxygen.
"
I have shown that the sedimentary beds deposited from this vast
freshwater lake attained a thickness of about eight thousand feet. The
lake itself, therefore, probably equalled that depth. (?) Now the
experiments of Wyville Thomson and Carpenter, made during the voyage
of the Lightning and the Porcupine, proved that at a
depth of three to four hundred fathoms, the pressure is equal to half a
ton on the square inch ; at a mile to one hundred and fifty-nine
atmospheres, and at seven thousand feet it amounts to two hundred
atmospheres, or four times the pressure under which Faraday liquefied
carbonic acid gas, the temperature at such great depths being very few
degrees above freezing point. In the carbonic acid gas generated from
the carbonaceous shales by heat, and interspersed as gas bubbles in the
cavities of the viscid, ferruginous amygdaloid, and in the admixture of
steam, lava, and ashes known as the ' Kimberley Blue' — reduced to the
liquid state by the enormous pressure in the subaqueous volcano — we
