Xiaomen Natural Monument Introduction
Xiaomen Islet is surrounded by the sea, shaped by long-term waves and tides that create diverse coastal erosion formations. Among them, "Whale Cave" is an easily accessible sea-eroded arch in Penghu, formed by the erosion of waves that hollowed out the cliff, giving it the name of sea-eroded arch. If you walk inside the cave, you can also hear the dramatic sounds of the ocean. Additionally, the rock face along the circumnavigation trail exhibits distinct and complete rock layers, consisting of siliceous basalt columnar joints, peat layers, siltstone layers, and sulfur layers from top to bottom, known as the "Crater Lake Remains." Like Whale Cave, these formations are unique and rare, serving as excellent field materials for understanding the processes of coastal erosion and geological evolution, and both have been designated as natural monuments of Xiaomen. The Xiaomen area is also famous for the "Xiaomen Islet Formation," which, based on geological age analysis, can be divided into two layers: the upper layer is composed of bioclastic limestone formed from the remains of marine organisms, quartz grains, and small foraminifera cement, while the lower layer consists of interbedded iron-rich quartz sandstone or sandy mudstone, clearly exposed due to weathering. Because such geological features are most complete in the Xiaomen area, it is named the "Xiaomen Islet Formation."