Dykes are the traces left by the lava rising through the stratum, most of which are distributed deep underground in volcanic cratersthen exposed to the surface due to the erosion of the surrounding rock layers by wind, wavesrain. It is a typical lithofacies near the crater. When the basalt lava intrudes into the rock crevices, some of its dyke joints will take on a plate-like structure after cooling. Many dikes are exposed in the Penghu Islands,there are no certain rules for their direction. The main outcropping sites of the dikes are Dashibi, Gangdiwan, Kueibishan in Beiliao Village, Chihkanzaitou, Damaoyu, Dragon Sea-eroded Platform in Qimei Township, Niumuping,so on. Exposed in Huayu are quartzite dykesrhyolite dykes. Specimens collected by this center are from Sisi Village, Huxi Township.