The Penghu archipelagos are made of basalt rocks and coral reefs. They are noted for the pillar basalt formations and white beaches of shells and sands. In particular, the pillar basalt formations are extremely rare in the world, thus full of values in terms of natural beauty, education and academic research. The pillar basalt formations are mostly products of volcanic activities. The melted basalt lava solidified around 1000 0C. The cracks cutting the pillars into hexagons were formed at the time of solidification and contraction, similar to cracks on dried cement blocks. The sites of these rock formations are now designated as natural conservation areas by the Council of Agricultural Affairs in accordance with the Cultural Assets Preservation Act. These sites include the Bird Island, Yuanpei Island, Chishan Island, Tingko Island, Little Baisha Island and Hsipei Island.