On the wave-cut platform of the Nima coast, where green tuff can be seen, two large tree fossils (silicified wood) lie exposed. They have been designated as natural monuments of the prefecture. Running through the cracks are veins of small, tightly packed quartz crystals. Quartz is a mineral made up of silicon dioxide, and although the silicified trees retain the appearance of trees, their components have been almost entirely replaced, and they are now masses of silicon dioxide minerals such as quartz and agate.