Stratigraphy: Early Cretaceous volcanic rocks with ages of approximately 140.9 ± 0.2 million years before present.

Distribution: The High Island Formation crops out in the Sai Kung and Clear Water Bay districts in eastern New Territories.

Lithology: Dominantly welded fine ash vitric tuff with minor tuff breccia and tuffaceous sandstone.

(Columnar-jointing in the High Island Formation, North Nine Pin Island)