http://b4hntuy3fimfh2227vf4f74emnya7p35i5brtqujs6leqvtclfwvjbqd.onion/doc/physics/diamonds-crookes/The%20Project%20Gutenberg%20eBook%20of%20Diamonds,%20by%20William%20Crookes..html
The
eruptive force was probably steam or
water-gas, acting under great pressure, but
at no high temperature. According to
Mr. Dunn, in the Kimberley Mine, at a
depth of 120 feet, several small fresh-water
shells were discovered in what appeared
to be undisturbed material.