ABSTRACT
No. 236 in 1971. A total of 17 km of passages has been mapped in the many caves in this area. This cave system is well known for its abundant carbonate speleothems. Microcoquina sand dunes are widely distributed in the Hallim district, overlying the cavernous Pyosonri basalt. Carbonate-bearing groundwaters percolated into the Hyop-jae cave system and deposited carbonate speleothems (dripstone, flowstone, and other speleothems) which cover the bare lava walls and coexist with lava speleothems (Kashima et al., 1989).
