Eocene Sierra Blanca limestone was described by the late Marvin Francis Keenan of the Leland Stanford Junior University,1 in carrying on work begun by R. N. Nelson. The Sierra Blanca limestone exposed for about seven miles on the south side of the San Rafael Mountains in Santa Barbara County, California, reaches an elevation of 4700 feet at the top of Sierra Blanca Mountain.2 In the valley of Indian Creek, a northerly branch of the Santa Ynez River, a thickness of 225 feet is exposed, affording a convenient place for the collection of samples. Keenan took this as the type locality. Elevation at this point ranges from 3000 to 3300 feet. Keenan states that the lower 160 feet of this deposit “are composed of dense, fine-grained buff to white-colored, almost pure limestone characterized by its high content of calcareous algae.” He gives the following summary of the paleontologic characters of . . .