To form and perfect the finer crystals, extremes of heat or cold appear to be necessary: whereas our clime has perhaps always been temperate. Beside this, it is probable that the mother-earth is not found pure with us. There is a kind of white clay, called “kaolin,” obtained in one particular quarry near Meissen in Saxony, and met with nowhere else. From this clay the exquisite Dresden porcelain is baked, and this clay cannot be exactly imitated. A near approach to it has been made by mixing good potter’s clay with pounded chalcedony-flints; but still the _biscuit_ so produced is never equal to that from the “kaolin.” In like manner, we may suppose that the peculiar earth which exists in sapphires no longer occurs in our post-tertiary clay-beds. Moreover, we know that there are many different clays occurring in our geological strata. We have the clays of the Lower Tertiary; the clay of the Wealden; and the Kimmeridge and Oxford clays, both of which belong to the Oolite. Also in these main divisions, sundry mineralogical varieties are comprised under a common name. But the great age of the granite formation renders it certain that from none of these clays could those sapphires have come (as to their _base_), which are born of the granite rock. Indeed, our existing beds of clay are more or less mingled with felspar, and felspar is one of the “silicates;” whereas the blue sapphire is pure alumina free from all admixture of silica. However this may be, the great fields for gems are in India and the island of Ceylon, and in certain parts of the Russian dominions. No very valuable stones have as yet been obtained from Australia; although the vicinity of gold-mines has always been held to be prolific in at least one kind: the “mother of ruby” being a roseate substance embedded in the rock, and generally met with alongside of a vein of gold. The topazes are not equal to those from Saxony. As to our own sea-girt Isle, it is surely as guiltless of indigenous gems, as of white elephants or birds of paradise. Had any such existed with us, they must long ere this have been brought to light and appeared in the market. We have bored the plain to two hundred fathoms’ depth: we have pierced the hillside in tunnels which extend for miles: geologists and antiquarians have delved and hammered and sifted: many curious fossils have turned up, and a world’s wealth in minerals, but never anything like a diamond or an oriental sapphire.