o differences in the rate of freezing, in the texture of the mud and probably in variations in water content of the mud. Some crystals in the locality from which these specimens came, show pinnate secondary growths. Specimens shown here are from near the upper part of the Eagle Ford at a point about two miles north from the Chisos Mining Company's property. Brewster County, Texas. Slightly reduced.
[Illustration: PLATE VII]
Plate VIII. Photograph of a cast made by pouring plaster over a surface of mud in which ice crystals had recently formed, in Rock Island, Illinois, after the ice in the crystals had been removed by slow natural sublimation into the atmosphere, leaving open cracks in the mud. The comb-like ridges on the plaster cast have the form of the ice crystals. Compare with Plate III.
[Illustration: PLATE VIII]
Plate IX. Photograph of a cast made by pouring plaster over a surface of mud in which ice crystals had formed, in Rock Is