Abstract: X-ray and chemical analyses were made of two soil clays from Colorado. X-ray diffraction analysis of glycerol-solvated samples oriented in parallel gave poor diffraction patterns. Randomly oriented powder x-ray diffraction analysis showed an intense 4.45 A band indicating the predominance of layer silicates. Total potassium analysis confirmed the presence of illite. Cation-exchange capacity and specific-surface measurements showed that high-charge layer silicates were present. The effect of differential cation saturation and differential heat treatment on the x-ray diffraction patterns of parallel oriented samples suggests interstratification of layer silicates in these soil clays.