arborescent substance adhering to some trap-rock. In its arborescent form,
this substance singularly resembles some of the branched species of
Nullipora. Under the blowpipe, it behaves like the specimens from
Ascension; but it is less hard and glossy, and the surface has not the
shrunk appearance.


CHAPTER III.--ASCENSION.

Basaltic lavas.
Numerous craters truncated on the same side.
Singular structure of volcanic bombs.
Aeriform explosions.
Ejected granitic fragments.
Trachytic rocks.
Singular veins.
Jasper, its manner of formation.
Concretions in pumiceous tuff.
Calcareous deposits and frondescent incrustations on the coast.
Remarkable laminated beds, alternating with, and passing into, obsidian.
Origin of obsidian.
Lamination of volcanic rocks.

(MAP 2: THE ISLAND OF ASCENSION.)

This island is situated in the Atlantic Ocean, in latitude 8 degrees S.,
longitude 14 degrees W. It has the form of an irregular triangle (see Map
2), each side being about six miles in length. Its highest point is 2,870
feet ("Geographical Journal" volume 5 page 243.) above the level of the
sea. The whole is volcanic, and, from the absence of proofs to the