About 350 million years ago, in the early Carboniferous period, a shallow tropical sea covered the region. Shellfish and coral remains accumulated on the floor of this sea. When the sea level began to fall, lush vegetation became established in coastal swamps, while dead plant material accumulated on the muddy swamp floor.
Deep burial of these sediments turned the shelly sediment to limestone and the swamp sediment to siltstone. The plant material became coal. Later, heat and pressure within the Earth turned the limestone into marble, recrystallising and destroying the shellfish remains. The siltstone became schist and the coal became graphite.
Today, Hong Kong marble is only found underground, while schist containing graphite is found in the northwest of Hong Kong.
Credit : History Museum of HK.
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