UNINHABITED REGIONS 
973 
underlying stone from disintegration, and had been the 
means of preserving the isolated beacon-like pyramids, 
so that they commanded the whole of the tableland, being 
visible to a great distance. The earth around their bases 
was strewn with fragments of tuff of different sizes, looking 
like black spots on a red background ; and as we advanced 
further, we observed fragments of the same rock, but less 
black in colour, scattered a long distance over the red 
sand. The tuff, which was inclining to violet, contained 
an abundance of vesicles, was almost as porous as a 
sponge, and rang sharply when struck with the hammer. 
Several hours later we could still see the fiery red gleam 
of the curious mountain -cones, with their raven-black 
caps. 
On the south side of the Arka-tagh we encountered 
several similar groups of isolated table-mountains. 
