The white organic shale exposed at Monterey was the first geologic formation of California to be described. It is largely composed of the siliceous skeletons of diatoms; radiolarians, silicoflagellates, foraminifers, fish remains, and mollusks occur in smaller quantity, the amounts being in the order named. Some difficulty has been experienced in identifying the formation elsewhere in the state on lithologic grounds and several synonymous or partially synonymous names have resulted. The bibliography indicates that most of the work on the paleontology of the formation has been done in Europe. The Monterey shale is of Miocene age and the top represents the last accumulation of pure, siliceous, organic strata in California. Unfortunately, however, there are vast quantities of such sediment in the state in a lower position in the geologic column than anything found in the Monterey section. Most of the oil in California is generally believed to have had its source in the organic constituents of the Monterey shale.