MR. F. A. BANNISTER: The so-called “thermokalite” and the existence of sodium bicarbonate as a mineral. The composition of a large collection of saline incrustations collected by Dr. Johnston-Lavis about 1889, has been investigated. He labelled them “thermokalite” but they are found to be a mixture of trona, thermonatrite, thenardite, and free sodium bicarbonate; no potassium salts are present. The name nahcolite is proposed for naturally occurring sodium bicarbonate. These incrustations were found lining the walls of a cuniculus near the Stufe de Nerone, Baia, Naples, Italy; their mode of occurrence is discussed from a physical-chemical point of view.