CURIOUS EROSION IN TENNESSEE CLAYS 481 



spaced (15-20 per square foot). Thin fragments of hardpan (fer- 

 ruginous sandstone) commonly form the protective capping and 

 are derived from the overburden. Other substances, such as 

 leaves, bits of wood, and concretions, function in the same way. 

 In short, any small, flat piece of coherent matter will do. These 

 miniature hoodoos are very abundant in this region and are espe- 

 cially characteristic of very plastic clays. 



