Eighteen samples of the Great Oolite series (Jurassic) were collected from various parts of the Crowley Road quarry, Witney, Oxfordshire, England, and analyzed for clay and carbonate content to see if a relation of composition to the type of rock resulting from recrystallization exists. It is suggested that where carbonate predominates over clay, a cohesive mass results, but in the reverse, the result is a plastic sediment when wet. Marls have a carbonate-clay ratio of less than four, but a small shift in this ratio could mean a change to a limestone. The term "marl" is defined as a mixed rock containing clay minerals and aragonite or calcite, usually together with accessor components, such as silt, in lesser quantity. It is friable when dry and plastic when wet.