The clay is sufficiently tenacious to give a considerable degree of consistency to the soil.

The internal structure of the hills, as revealed by the deep wells, is similar to that already described.

The alternate layers of clay and sand, as well as the oxide of iron, which forms in its various combinations a cement to the sand, allow of extensive tunneling.

The prisoners not only constructed numerous dirt huts with balls of clay and sand, taken from the wells which they have excavated all over those hills, but they have also, in some cases, tunneled extensively from these wells.

The lower portions of these hills, bordering on the stream, are wet and boggy from the constant oozing of water.