The Caballos Novaculite bears many evidences of a peritidal origin. The lower white novaculite contains a bed with spectacular bird's-eye structures greatly resembling those found in peritidal carbonate muds. Internal sediment was pumped through a ramifying cavity system. Both this novaculite and the upper drab chert member show textures produced by replacement and solution of evaporite nodules; breccias thought to be due to evaporite solution collapse are present. Lack of diluting clay, and low content of potassium and manganese in the normal novaculite argue for a shallow hypersaline lagoonal origin, rather than a deep, open-sea ooze. Lenticularity of facies, and the great differences between spicule-rich white novaculite and radiolarian-rich drab chert, argue for depos tion in separate shallow environments rather than in a deep sea. Flat-pebble conglomerates in the drab radiolarian cherts are similar to tidal-flat conglomerates in carbonate rocks. A trinitarian occurrence of giant fossil logs, red jaspers (probably silicified paleosoils), and fossilized algal/fungal filaments indicates subaerial exposure of the upper beds of the Caballos. The white novaculites formed in bays with occasional hypersaline tendency and cut off from influence of muddy river waters. The drab, clayey radiolarian cherts formed in shallow-marine environments muddied by river influx.