Plate IV. Photograph of fossil casts of ice crystals seen on some 

 stony flags in the upper part of the Eagle Ford at Fossil Knobs, 

 about two miles northwest of the Chisos Mine in Brewster County, 

 Texas. These may be characterized as relatively short and scattered. 

 This shows ridges projecting into the grooves formed by ice crystals 

 on the surface of a muddy layer originally underlying the layer photo- 

 graphed. Slightly reduced. 



