THE GEOLOGY OF THE CHINCHAS ISLANDS. 
179 
to the top is obtained by clambering up the face of a steep rock, and 
over a very fine natural bridge. Close to the landing-place there is 
a narrow gulley in the rocks, through which a great mass of ammo- 
niacal incrustation has run and spread itself over the whole face of 
the cliff; it has also concreted in the gulley, nearly completely filling 
it up with a stalagmite-form mass, resembling a frozen cascade. The 
origin of this is rather obscure. The whole of the cliff here is capped 
with the coarse trap and granite conglomerate, beneath which a small 
bed of very fine yellow sandstone (not met with elsewhere on the 
island) occurs; this is exceedingly limited in its extent, and lies on 
the granite; the coarse gravel grit takes its place a little higher up 
the hill: no traces of the shell breccia are found. The other geolo¬ 
gical characters of the island are similar to those of the north island. 
The greenstone protrusions are larger in extent, and the granite, 
especially the cliffs on the western side of the island, exhibit that 
curious unconformability between its upper and lower portions al¬ 
ready mentioned; on this side the granite might at a distance be 
easily mistaken for a stratified rock, the surface of the rock being 
curved down towards the water’s edge, its section exhibiting a sys¬ 
tem of joints which accurately follow the line of the curve above. 
The only sandy bay in it occurs on the eastern side, and is de¬ 
cidedly the best place for studying the greenstone, a square pro¬ 
trusion of considerable size occurring here. The south side of the 
cove is ordinary granite, which gradually passes into the greenstone; 
the junction of the two on the north side cannot be traced, owing to 
a large bed of fine sandstone grit which fills up the valley between 
them. The sea is evidently encroaching on this bed of grit, and 
it appears different in its external characters from the beds described 
in the North Island, and also in the fact of its not resting on the coarse 
conglomerate. There is a small bed of similar character in one of the 
coves looking south-east on the North Island, which is there also 
associated with the greenstone. 
The guano rests on the grit. The hill here is excessively curious, 
its summit covered with remains of sea-lions {Otariajubata) in scores. 
This island had not been worked whenl visited it; therefore, I can say 
nothing concerning its surface. The trap is not so abundant in this 
island, the greenstone apparently taking its place; the summits of 
some of the highest cliffs are capped with greenstone. 
These are the principal observations I was enabled to make re- 
