524 
ASCENSION 
CHAP. 
explanation. The intervening spaces are concealed with layers 
of pumice, ashes, and volcanic tuff. Whilst passing this end of 
the island at sea, I could not imagine what the white patches 
were with which the whole plain was mottled ; I now found 
that they were sea-fowl, sleeping in such full confidence, that 
even in mid-day a man could walk up and seize hold of them. 
These birds were the only living creatures I saw during the 
whole day. On the beach a great surf, although the breeze was 
light, came tumbling over the broken lava rocks. 
The geology of this island is in many respects interesting. 
CELLULAR FORMATION OF VOLCANIC BOMB. 
In several places I noticed volcanic bombs, that is, masses of 
lava which have been shot through the air whilst fluid, and have 
consequently assumed a spherical or pear-shape. Not only 
their external form, but, in several cases, their internal structure 
shows in a very curious manner that they have revolved in their 
aerial course. The internal structure of one of these bombs, 
when broken, is represented very accurately in the accompanying 
woodcut. The central part is coarsely cellular, the cells 
decreasing in size towards the exterior ; where there is a shell¬ 
like case about the third of an inch in thickness, of compact 
stone, which again is overlaid by the outside crust of finely 
cellular lava. I think there can be little doubt, first, that the 
external crust cooled rapidly in the state in which we now see it ; 
