But all the stones or gems valued thus are not ex¬tracted from the earth. A few are found in strange places and have a more mysterious origin. Two of these deserve special attention, the pearl and amber.

Pearls are morbid growths or cysts found in many shells, particularly in those of the oyster and mussel but the best come from the pearl-oyster or Oriental pearl-mussel around the shores of the Persian Gull Ceylon, Burma and Venezuela. During recent years private enterprise has been centred upon the South Pacific as a pearling ground, and several 150-ton schooners and numerous thirteen-decked boats are employed.

From the. time of Pliny the pearl-fishing grounds of the Persian Gulf and around Ceylon have been cele¬brated, and many were the speculations as to the cause of the existence of pearls in the shell-fish. Until recently they were thought to be due to irritation caused by boring sponges or tapeworms, but special examina¬tions by experts of over 30,000 pairs of separated valves prove that these animals have little influence in pearl production. Quite 90 per cent, are due to the attach¬ment of cysts to the nacreous lining of the shell, which Dr Lyster Jamieson maintains is caused by the im¬migration of the epidermis into the tissues. Pearls have skins, like onions, and a bad lustre can be improved by “skinning” and the value thus enhanced by about £100.

At one time pearls of considerable value were found in the mountain streams of Britain and Canada, and the Scottish and Irish pearl fisheries were flourishing industries.

Pearls have three layers, like the shells, but the innermost layer of the shell becomes the outermost in the pearl.
In Ceylon the oyster is found in shallow and well-sheltered waters. In the Mergui district of Burma it lives at greater depths, is exposed to rapid currents and is reproduced less rapidly. The Mergui pearls are, however, above the average in size and appearance, and ordinary single pearls from this district realised from £300 to £1600 before the war. In 1919 a few special stones were sold at £5000 to £6000 each. Mergui mother-of pearl is also of the best quality, and more than eighty tons of this commodity are annually exported.