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and are sometimes accompanied by pockets or nodules of calcite, aragonite, strontianite, celestite, and epsomite.

The upper third of the formation, as seen at the top of Mount Bonnel, presents alternations of friable marls and hard limestone strata. The limestone strata usually average less than a foot in thickness. These alternations occur with great regularity and persistence. Clay is the chief accessory of the calcareous beds. The marls are soft and laminated and are composed largely of minute shell fragments, giving the beds a distinctly granular, oolitic character. They have little clay and imbibe the moisture very freely.

While possessing no great agricultural possibilities, the basal or alternating beds are capable of producing valuable building material, among which are building stones. Some of these have rich "magnesian" buff yellow colors, while the limestones often resemble the stones of Caen, France, which are imported into this country. Some of the beds are also valuable for the manufacture of hydraulic cements, although at present they are not utilized. These rocks also contain undeveloped beds of epsom salts, strontianite, and other materials.

The alternations of horizontal beds of soft marls and hard limestones above described produce the bench and terrace topography of the slopes of many of the canyons and along the margin of the Edwards Plateau from the East Fork of the Nueces to the Colorado, where the streams have cut downward through