Xiaomen Natural Monument Introduction
Xiaomenyu is surrounded by the sea, and has been shaped by waves and tides over time, creating a variety of sea erosion terrains. Among them, the "Whale Cave" is an easily accessible sea erosion arch in Penghu where visitors can observe its formation due to wave erosion penetrating the cliffs, creating a hollow structure, thus earning its name as a sea erosion arch. Inside the cave, one can hear the stunning sound of the waves. Furthermore, along the island trail, the rock walls exhibit distinct and complete rock layers. From top to bottom, these layers consist of silica basalt columnar jointing, peat layers, siltstone layers, and sulfur layers, collectively known as the "Crater Lake Remains." Like the Whale Cave, it possesses rarity and uniqueness, and both serve as excellent field teaching materials for understanding the processes of coastal erosion and geological evolution, which is why they have also been designated as natural monuments in Xiaomen. The Xiaomen region is also famous for the "Xiaomenyu Formation," which, based on geological age analysis, can be divided into upper and lower layers. The upper layer consists of shell limestone formed by the remains of biogenic shell debris, quartz grains, and tiny foraminifera cement, while the lower layer is an interbedding of iron-rich quartz sandstone or sand-mudstone that exposes clearly defined rock layers due to weathering. Due to this geological characteristic, the Xiaomen region exhibits it most completely, thus named the "Xiaomenyu Formation."
