My interest in amygdules and cavity-fillings was stimulated by the study of certain dikes in the coal mines of Linsi, Chihli province, north China, on which a report was written for M. F. F. Mathieu, then geologist for the Kailan Mining Administration. Later, cavity-fillings and masses of alteration products were seen in other dike rocks from the Liukiang coal-fields, and from near Chaochiakou. Open cavities in a granite from Mukden and in a remarkable contact rock from Tsinanfu in Shantung were studied, as well as a thick amygdaloid in the Western Hills of Peking. After reviewing the available literature, it seemed to me that a paper which would suggest a genetic classification of cavities and cavity-fillings would be acceptable. Such a classification is offered in this paper and is illustrated with examples which came within my own observation, and with comments upon some published examples, and with one case . . .