• "This unit is easily differentiated from others as it is composed of rather thin layers (20 to 30 centimeter thick) of even-bedded, dull-red claystone with numerous thin interbeds of gray claystone. The basal and uppermost layers of the Upper Red Bed, like those of the Lower Red Bed, are not red. The most significant mineralogical feature displayed by the Upper Red Bed is the presence of bentonite, which constitutes some 35 per cent of the material composing the beds. Montmorillonite is evidently the constituent mineral, as the clay swells and slumps when placed in water. Quartz is present as extremely small rounded grains and constitutes about 60 per cent of the detrital fraction. Muscovite is also present. The red limonite stain is not soluble in cold hydrochloric acid but is completely soluble in hot hydrochloric acid. After the stain is dissolved, the clay residue is the same greenish-gray color as the upper and lower beds of this unit, indicating that all but the middle layers were probably leached before or shortly after deposition. The presence of bentonite is significant, for only in the unit below the Upper Red Bed are there any traces of volcanic materials." Lithological description taken from Fields (1959): Geology of the La Venta Badlands Colombia, South America. Vol 32, 405-444.