The sedimentary ironstones of Liassic and Oolitic ages vary in the state of oxidation of their iron content from ferrous in the green ores to ferric in the red-brown ores which have undergone weathering at deposition or on exposure. Taylor (1) has surveyed the principal physical, chemical and mineralogical changes which accompany weathering. Loss of lime, magnesia, alumina and carbonate takes place during the oxidation of iron. Previous workers have attributed the formation of kaolinite, sericite or hydrous mica, goethite and “clay” to the alteration of the chamosite which occurs in the parent ore. Recent research (2) on the properties of chamosite has enabled a fresh approach to be made to the study of weathered ironstones.