THE FEATURES AND FORMATION MECHANISM OF ACID VOLCANIC BOMBS IN THE SANDAOGOU AREA, NORTHERN HEBEI

This paper for the first time reports the discovery of Late Jurassic acid volcanic bombs in the Sandaogou area, northern Hebei. The bombs have a typical external feature and a perfect internal struetnre, Investigations have confirmed that acid volcanic bombs do exist in nature and are not produced only by intermediate and basic magmas. The author has preliminarily summed up four criteria for identifying acid voleanie bomds.