A mountain spring and gold sand

　　A small mountain spring ran tinkling down the narrow stone crevices. Many years passed. An egg-sized shallow hole was washed out on the rock. Strangely, the mountain spring anyhow brought some bright yellow gold sand and got to fill the small hole.

　　One day, an old woodcutter hit on this secret. To his amazement, he cupped the gold sand carefully.

　　Since then, the old man furtively fetched the gold sand once every half a month or so, so he became rich soon.

　　When discovering his father's secret, his son advised:If they widened the stone crevice for more mountian spring, more gold sand could be washed here. The old man thought it over and felt it advisable. So the father and son chiseled the narrow stone crevise so widely that the mountain spring was several times than ever. But unexpectedly, the gold sand didn't increase but disappeared ever since.

　　They felt puzzled: Where had the gold sand gone?