CHAPTER II.
	MODES OF ORIGIN. The origin of each gem will be dealt with in its proper place, but here again a few general points may be noticed. It is well worth the reader's while to study such a book as that of Robert Boyle's above referred to, to gain an insight into the earnest endeavours these old scientists made to dis­cover the how, why, and wherefore of Nature's working. Aristotle in the third book of Meteors states bis belief that the infusible stones were made by a " dry exhalation " ; another theory was that they were formed of a mixture of earth and water congealed by cold ; later again the almost universal belief was that they originated from the actual fusion by heat of various earthy matters. Boyle, by careful " examens " of different chemical substances, as alum, salt, saltpetre, etc., in the process of crystallisation, came to the conclusion that all gems originated from crystallisation from a watery solution ; he came to the conclusion that for the particles, of which the mineral was composed, to be able to move into their proper places so as to unerringly build up a crystal of a definite geometrical form, these particles must have existed in a fluid state of some sort. Crystals are formed either by sublimation, solidification from a molten mass, or separation from a solution, and it is quite possible one of the commonest ways of formation of the crystals of mineral substances is by separation from