In my opinion, Margaret, that substance was once the head of a comet." "What is the substance ?" she asked, hastily.
"It is a mass of solid diamond!" Margaret screamed.

She could not say one word.
"Yes," said he, "I believe the whole central portion of the earth is one great diamond.

When it was moving about in its orbit as a comet, the light of the sun streamed through this diamond and spread an enormous tail out into space; after a time this nucleus began to burn." "Burn!" exclaimed Margaret.
"Yes, the diamond is almost pure carbon; why should it not burn?
It burned and burned and burned.

Ashes formed upon it and encircled it; still it burned, and when it was entirely covered with its ashes it ceased to be transparent, it ceased to be a comet; it became a planet, and revolved in a different orbit.

Still it burned within its covering of ashes, and these gradually changed to rock, to metal, to everything that forms the crust of the earth." She gazed upon him, entranced.
"Some parts of this great central mass of carbon burn more fiercely than other parts.