of Plato on the origin of non-metallic mineral substances than those of Aristotle. Plato believed4 that ordinary stone was formed when, in a mixture of earth and water, the latter changed to a form of air and rose to its own region; in doing so it gave a thrust to the surrounding air, which reacted on the remaining earth and compacted it into stone. He also thought, however, that certain kinds of stones were composed of a combination of earth and water,5 and this idea is accepted by Theophrastus as shown by his statements in sections 9 and 10. But according to Aristotle, infusible stones were formed by the dry type of exhalation acting on earth,6 though certain fusible stones were, like the metals, more of the nature of water.7
1. stones, including the more precious kinds. The distinction here, as shown by subsequent passages, is primarily between the stones which occur in large masses in the form of rock and the various minerals of limited size and distinctive properties, particularly those that were used for seals.
1. the metals have been discussed in another place. Probably this refers to Theophrastus' lost work on mines8 mentioned by Diogenes Laertius.9
2. as has been explained above.
Though this appears to be a reference to a preceding passage that has dropped out, the close and logical development of the discussion up to this point seems to leave no room for the introduction of any other statement. Possibly this refers to a discussion in the lost treatise on mines mentioned by Diogenes Laertius or to a passage in some other treatise that may have immediately preceded the present one in the books of Theophrastus as they were originally written.
From the rather vague statements in this section it would appear that Theophrastus was somewhat more advanced than his predecessors in his theories about the formation of mineral substances; these tended even to approach modern views on the formation of minerals by crystallization from magmatic or aqueous solutions.
*Timaeus, 6oC. ^Timaeus, 61. β Meteorologica, III, 6.
7 Meteorologica, IV, ίο. 8 Ilepl μετάλλων. 9 V, 44.
