(Read, September, 1947, at a Joint General Meeting with the Teeside Section of the Royal Institute of Chemistry). EVAPORITES BY S. E. HOLLINGWORTH I should like first of all to express my pleasure that the subject of “Evaporites” has been chosen for this joint discussion and also to thank you for asking me to take part. Rocks formed by precipitation are among the most intriguing in the earth’s crust. In Britain our knowledge of their petrology and regional variation is distinctly meagre. In the early period of active exploration by boring valuable records were published by Marley, but there was little or no petrographical study of the detail of the cores, and, since Marley’s paper, there has been little detailed work until quite recently. The study of salt deposits is handicapped by the fact that they are usually found at considerable depths and are not, of course, available for field study in this humid climate. The position is less difficult in the case of gypsum and anhydrite deposits, as these are quarried and mined as solid rock, whereas salt is obtained in the form of brine. Geologists in this country, from the time of Sorby onwards, have been well to the fore in the study of detrital sediments and the evidence they yield of the earth’s history. They have expended much energy, thought and expense of chemical analyses in delving into the complexities of the crystallisation and variation of igneous rocks—subjects of great scientific interest. The chemical reactions and …