Phong
Nha - Ke Bang can be compared to a huge geological museum thanks to its
complicated geological structure with different categories of stone
including sandstone, quartz, schist, siliceous limestone, granite,
granodiorite, diorite, applet, pegmatite, etc. Phong Nha-Ke Bang is the
oldest and largest tropical karst formed 400 million years during the
main geological periods of the Earth.