Sandstone rocks stand up in it at various points like islands, but all are metamorphosed, and branches have flowed off from the igneous sea into valleys and defiles, and one can easily trace the hardening process of the fire as less and less, till at the outer end of the stream the rocks are merely hardened.

These branches equal in size all the rocks and hills that stand like islands, so that we are justified in assuming the area as at least 100,000 square miles of this basaltic sea.
The molten mass seems to have flowed over in successive waves, and the top of each wave was covered with a dark vitreous scum carrying scoriae with angular fragments.

This scum marks each successive overflow, as a stratum from twelve to eighteen inches or more in thickness.

In one part sixty-two strata are revealed, but at the Victoria Falls (which are simply a rent) the basaltic rock is stratified as far as our eyes could see down the depth of 310 feet.

This extensive sea of lava was probably sub-aerial, because bubbles often appear as coming out of the rock into the vitreous scum on the surface of each wave: in some cases they have broken and left circular rings with raised edges, peculiar to any boiling viscous fluid.