Rock-gypsum occurs as extensive deposits of considerable economic importance in the neighbourhood of Nottingham. The mode of occurrence and origin have been studied by several geologists, to whose work references were given in a recent communication to this Society. I Investigations have proceeded chiefly on field lines and microscopic examination has been somewhat neglected, except with respect to the contact relations of gypsum and anhydrite. Nevertheless, examination of thin slices from specimens collected in different parts of the district yields information of considerable interest and. it may be, of importance.