Xiao Men Natural Monument Introduction
Xiaomen Islet is surrounded by the sea and has been shaped by the long-term effects of waves and tides, resulting in a variety of sea erosion landforms. Among them, "Whale Cave" is an easily accessible sea-eroded arch in Penghu, formed by the erosion of sea waves that hollowed out the cliff, hence it is called a sea-eroded arch. If you walk inside the cave, you can also hear the impressive sound of the waves. Additionally, the rock wall next to the circular island trail reveals distinct and complete rock layers, consisting of silica basalt columnar joints at the top, followed by peat layers, sandstone layers, and sulfur layers; this is known as the "Volcanic Lake Remnant." Like Whale Cave, it possesses rarity and uniqueness, making it an excellent field study resource for understanding the process of sea erosion and geological evolution. Thus, it has also been designated as a natural monument of Xiaomen. The area is also famous for the "Xiaomen Islet Formation," which can be divided into two layers based on geological age analysis. The upper layer consists of shell limestone formed from biological shell remains, quartz grains, and small foraminifera cemented together, while the lower layer consists of interbedded iron-rich quartz sandstone or siltstone, exposed clearly due to weathering. This geological feature is most completely revealed in the Xiaomen area, thus named the "Xiaomen Islet Formation."
