THE DIAMOND.                                       171
	answer a good purpose, since they often lead the way to truth. But this is not all ; they illustrate the ingenuity of the human mind in seeking to account for the methods Nature takes for the accomplishment of her secret operations. Some of these theories about the origin of the diamond are very ingenious and interesting, though the amount of truth they embody remains to be proved. It has been suggested that the vapors of carbon during the coal period may have been condensed and crystallized into the diamond ; and again that itacolumite, generally regarded as the matrix, was saturated with petroleum, which, collecting in nodules, formed this gem by gradual crystallization. Newton believed it had been a coagulated, unctuous substance, of vegetable origin, and was sustained in his theory by many eminent philosophers, including Sir David Brewster, who believed the diamond was once a mass of gum derived from certain species of wood, and that it subsequently assumed a crystalline form. Dana and others advance the opinion that it may have been produced by the slow decomposition of vegetable material, and even from animal matter. Burton says it is younger than gold, and suggests the possibility that it may still be in the process of formation, with capacity for growth. Specimens of the diamond have been found to enclose particles of gold, an evidence, he thinks, that its formation was more recent than that of this precious metal. The theory that the diamond was formed immediately from carbon by the action of heat is opposed by another, maintaining that it could not have been produced in this way, otherwise, it would have been consumed. But the advocates of this view were not quite on their guard against a surprise, for some quick-witted opponent found by experiment that it will sustain great heat without combustion. Later opinions incline to the hypothesis that the diamond