O.Westwood." In passing along we see every where the power of vegetation in breaking up the outer crust of tufa.

A mopane-tree, growing in a small chink, as it increases in size rends and lifts up large fragments of the rock all around it, subjecting them to the disintegrating influence of the atmosphere.

The wood is hard, and of a fine red color, and is named iron-wood by the Portuguese.

The inhabitants, observing that the mopane is more frequently struck by lightning than other trees, caution travelers never to seek its shade when a thunder-storm is near--"Lightning hates it;" while another tree, the "Morala", which has three spines opposite each other on the branches, and has never been known to be touched by lightning, is esteemed, even as far as Angola, a protection against the electric fluid.

Branches of it may be seen placed on the houses of the Portuguese for the same purpose.